The Mysterious World of the Human Genome
The Mysterious World of the Human Genome
Frank Ryan
How could a relatively simple chemical code give rise to the complexity of a human being? How could our human genome have evolved? And how does it actually work?Over the past 50 years we have deciphered the inner workings of the human genome. From the basic structure of DNA through to the complete sequence of the code, what first appeared to be simple is actually a complex and beautiful three-dimensional world that makes each of us who we are.In The Mysterious World of the Human Genome acclaimed science writer Frank Ryan leads us through the most exciting scientific discoveries of the last 50 years, revealing how this science has unlocked the cure of some genetic diseases, developed the use of DNA in forensic science and paternity testing, helped us trace our ancestors and provided a definitive map for the movement of humans out of Africa. This scientific journey has had a profound impact on our understanding of the evolution of life itself, through the role of the most ancient of organisms in our basic biology all the way to the revelation that our most recent ancestor, Homo neanderthalensis, lives on in many of us.In the ever more complicated world of the human genome, this is the first book to explain how the human genome actually works as a whole and how that knowledge will have a profound effect on our understanding of where we have come from and where we are likely to be going in the future.
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William Collins
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Dedication (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
To Oswald T. Avery
Possibly I am a scientist because I was curious when I was young. I can remember being ten, eleven, twelve years old and asking, ‘Now why is that? Why do I see such a peculiar phenomenon? I would like to understand that.’
LINUS PAULING
Table of Contents
Cover (#u3af8175c-f258-5aef-b829-c7a1ebaacaf9)
Title Page (#ub5818fc8-1cfc-5065-b3d3-5c502ebf4ddd)
Copyright (#ue1d03a02-d5fb-5bb0-bc5e-8a44f220831e)
Dedication (#uad5cd499-705e-5b89-8db7-4bf4bdb35f4c)
Epigraph (#u4d5d602f-7992-5f18-b605-bfe44bdd4227)
Introduction (#u2416afec-85a4-5d0c-8645-3951116e978d)
Chapter One: Who Could Have Guessed It? (#u05e980ed-4d22-5d4a-8297-9b81da3b9238)
Chapter Two: Dna Is Confirmed as the Code (#u888a0706-a215-5ddb-b81a-cf7ffb4bafe5)
Chapter Three: The Story in the Picture (#ub36631bd-86c2-521b-aaeb-2af0e5d50298)
Chapter Four: A Couple of Misfits (#u81b62540-240a-52ea-91b6-64747f7b3270)
Chapter Five: The Secret of Life (#u4e6ea3b3-7aa6-5680-ae66-ab331263e1d9)
Chapter Six: The Sister Molecule (#litres_trial_promo)
Chapter Seven: The Logical Next Step (#litres_trial_promo)
Chapter Eight: First Draft of the Human Genome (#litres_trial_promo)
Chapter Nine: How Heredity Changes (#litres_trial_promo)
Chapter Ten: The Advantage of Living Together (#litres_trial_promo)
Chapter Eleven: The Viruses That Are Part of Us (#litres_trial_promo)
Chapter Twelve: Genomic Level Evolution (#litres_trial_promo)
Chapter Thirteen: The Master Controllers (#litres_trial_promo)
Chapter Fourteen: Our History Preserved in Our Dna (#litres_trial_promo)
Chapter Fifteen: Our More Distant Ancestors (#litres_trial_promo)
Chapter Sixteen: The Great Wilderness of Prehistory (#litres_trial_promo)
Chapter Seventeen: Our Human Relatives (#litres_trial_promo)
Chapter Eighteen: The Fate of the Neanderthals (#litres_trial_promo)
Chapter Nineteen: What Makes You Unique (#litres_trial_promo)
Chapter Twenty: The Fifth Element (#litres_trial_promo)
Bibliography (#litres_trial_promo)
Chapter Notes (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
By the Same Author (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
Introduction (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
No special act of creation, no spark of life was needed to turn dead matter into living things. The same atoms compose them both, arranged only in a different architecture.
JACOB BRONOWSKI,THE IDENTITY OF MAN
Bronowski begins his more famous book, The Ascent of Man, with the words, ‘Man is a singular creature. He has a set of gifts which make him unique among the animals: so that, unlike them, he is not a figure in the landscape – he is a shaper of the landscape.’ But why should we humans have become shapers of the landscape rather than mere figures inhabiting it? We differ from, say, a sea horse or a cheetah because our genetic inheritance, the sum of the DNA that codes for us, is different in humans when compared to the horse or the cheetah. We call this the genome, or, to be more specific in our case, the human genome.
Our genome defines us at the most profound level. That same genome is present in every one of the approximately 100,000 billion cells that make us who we are as individual members of the human species. But it runs deeper than that. In more personal terms, in myriad tiny variations that we each possess and are individual to us only, it is the very essence of us, all that, in genetic and hereditary terms, we have to contribute to our offspring, and through them to the sum total evolutionary inheritance of our species. To understand it is to know, in the most intimate sense, what it means to be human. No two people in the world today have exactly the same genome. Even identical twins, who will have been conceived with exactly the same genome, will have developed tiny differences between their genomes by the time of their births: differences that may have arisen in parts of their genomes that don’t actually code for what we normally mean by genes.
How strange to realise that there is actually more to our individual genome than genes alone. But let us put aside such details for the moment to focus on the more general theme. How could a relatively simple chemical code give rise to the complexity of a human being? How could our human genome have evolved? How does it actually work? Immediately we are confronted by mysteries.
To answer these questions we need to explore the genome’s basic structure, its operating systems and its mechanisms of expression and control. Some readers might react with incredulity. Surely any such exploration promises a journey into extraordinary complexity, one that is far too obscure and scientific for a non-scientist reader? In fact this book is aimed at exactly such a reader. As we shall see, the basic facts are easy enough to grasp, and the way to grasp them is to break the exploration into a series of simple, and eminently logical, stages. This journey will lead us through a sequence of remarkable revelations about our human history – even into the very distant past of our ancestors’ lives and their prehistoric exploration of our beautiful life-giving planet.
The exploration will raise other, equally important, questions, too. How, for example, does this extraordinary entity that we call the human genome enable our human reproduction – the fertilisation of our maternal egg with the paternal sperm? How does it control the quasi-miracle of the developing embryo within the mother’s womb? Returning to generalities for the moment, though, we can be sure that an important ingredient of the genome, and its essential nature, is memory – the memory, for example, of the totality of every individual human’s genetic inheritance. But how exactly does it perform this remarkable feat of memory? We know already that this wonder chemical we call DNA works like a code, but how could any code recall the complex instructions that go into the making of cells and tissues and organs, and then once made, bring them into function in the single coordinated whole that comprises the human being? Even then we have hardly begun to confront the mysteries of the human genome. How does this same extraordinary structure acquire the programming that gifts the growing child with the wonder of speech, that bestows the related capacity for learning, writing and education, and which makes possible the maturing of the newborn to the future adult, who then repeats the cycle all over again when he or she becomes a parent in turn?
The wonder is that all of this might be encompassed in a minuscule cluster of chemicals including, but not exclusive to, the master molecule we call deoxyribonucleic acid – or DNA. This chemical code somehow records the genetic instructions for making us. Built into that code must be the potential for individual liberty of thought and inventiveness, enabling every human artistic, mathematical and scientific creativity. It gives rise to what each of us thinks innately as our private inviolate ‘self’. Somehow that same construction of ‘self’ made possible the genius of Mozart, Picasso, Newton and Einstein. It is little wonder that we look at the repository of such potential with awe. No more is it surprising that we should want to understand this mystery that lies at the very core of our being.
Only recently have we come to understand the human genome in sufficient depth and subtlety to be able to put together its marvellous story – to discover, for example, that there is rather more to it than DNA alone. This is the story I shall attempt to convey in this book.
A few years ago I gave a lecture on a related theme at King’s College London. The chairman asked me if I planned to write a book about it. When I said yes, he asked me to please write it in words that a lay reader, like himself, could readily understand.
‘Just how simple do you want me to make it?’
‘I want you to assume that I – your reader – know nothing at all to begin with.’
This, then, I promise to do. There will be no complicated scientific language, no mathematical or chemical formulae or unexplained jargon, and I shall introduce no more than a handful of simple illustrations. Instead I shall begin from first principles and assume that the readers of this book know little about biology or genetics. Even non-biologists might recall the many surprises when the first rough draft of the human genome was announced to the world, in 2001.The discoveries since then have confirmed that a good deal of the human genome – in its evolution, structure and workings – is far from what we had earlier imagined. Those surprises do not diminish the importance of the wealth of knowledge that had gone before, but rather, like all great scientific discoveries, they enhance it. Thanks to this new understanding, humanity has entered what I believe to be a golden age of genetic and genomic enlightenment, which is already being extrapolated to many important fields, from medicine to our human prehistory. I think society at large deserves to understand this and what it promises for the future.
one (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
Who Could Have Guessed It? (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
The large and important and very much discussed question is: How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?
ERWIN SCHRÖDINGER
In April 1927 a young Frenchman, René Jules Dubos, arrived at the Rockefeller Institute for Medical Research, in New York, on what would appear to have been a hopeless mission. Tall, bespectacled and a recent graduate of Rutgers University, New Jersey, with a PhD in soil microbiology, Dubos had an unusually philosophical attitude to science. He had become convinced, through the work of eminent Russian soil microbiologist Sergei Winogradsky, that it was a waste of time studying bacteria in test tubes and laboratory cultures. Dubos believed that if we really wanted to understand bacteria we should go out and study them where they actually lived and interacted with one another and with life in general, in the fields and the woods – in nature.
On graduation from Rutgers Dubos had found himself unemployed. He had applied to the National Research Council Fellowship for a research grant but had been turned down because he wasn’t American, but somebody had scribbled a handwritten message on the margin of the rejection letter. Dubos would later reflect upon the fact that it was written in a female hand, almost certainly added as a kindly afterthought by the official’s secretary. ‘Why don’t you go and ask advice and help from your famous fellow countryman, Dr Alexis Carrel, at the Rockefeller Institute?’ Dubos duly wrote to Carrel, which brought him, in April 1927, to the building on York Avenue, on the bank of the East River.
Dubos knew nothing about Carrel, or indeed about the Rockefeller Institute for Medical Research, and was surprised on his arrival to discover that Carrel was a vascular surgeon. Dubos had no academic knowledge of medicine and Carrel knew nothing about the microbes that lived in soil. The outcome of their conversation was all too predictable; Carrel was unable to help the youthful microbiologist. Their conversation closed about lunchtime and Carrel did Dubos the courtesy of inviting him to have lunch with him in the Institute’s dining room, which had the attraction for a hungry Frenchman that they served freshly baked bread.
It seemed entirely by accident that Dubos found himself sitting at a table next to a small, slightly built gentleman with a domed bald head who addressed him politely in a Canadian accent. The gentleman’s name was Oswald Theodore Avery. Although Dubos later confessed that he knew as little about Avery as he did of Carrel, Professor Avery (his close associates referred to him as ‘Fess’) was eminent in his field, which was medical microbiology. It would prove to be a meeting of historic importance both to biology and to medicine.
Avery subsequently hired Dubos as a research assistant, in which role Dubos discovered the first soil-derived antibiotics. Meanwhile Avery led his small team – who were working on what he called his ‘little kitchen chemistry’ – on another quite different quest, one that would help unravel the key to heredity. Why then does society know little to nothing about this visionary scientist? To understand how this anomaly came about we need to go back in time to the man himself and the problems he faced three-quarters of a century ago.
*
In 1927, when Dubos first met Avery, the principles of heredity were poorly understood. The term ‘gene’ had been introduced into the nomenclature two decades earlier by a Danish geneticist, Wilhelm Johannsen. Curiously, Johannsen had adopted a vague concept of heredity, known as ‘pangene’, that was first proposed by Charles Darwin himself. Johannsen modified it to take on board the belated discovery of the pioneering work of Gregor Mendel, which dated back to the nineteenth century.
Readers may be familiar with the story of Mendel – the cigar-smoking, Friar-Tuck-like abbot of an Augustinian monastery in Brünn, Moravia (now the Czech Republic) – who undertook some brilliantly original studies of the peas he cross-bred in the monastery vegetable garden. From these studies Mendel discovered the basis of what we now know as the laws of heredity. He found that certain characteristics of the peas were transmitted to the offspring in a predictable manner. These characteristics included tallness or dwarfishness, presence or absence of the colours yellow or green in the blossoms or axils of the leaves, and the wrinkled or smooth skin in the peas. Mendel’s breakthrough was to realise that heredity was stored within the germ cells of plants – and this would subsequently be extrapolated to all living organisms – in the form of discrete packets of information that somehow coded for specific physical characters or ‘traits’. Johannsen coined the term ‘gene’ for Mendel’s packet of hereditary information. At much the same time, a combative British researcher, William Bateson, extrapolated the term ‘gene’ to the discipline he now called ‘genetics’ to cover the study of the nature and workings of heredity.
Today, if we visit the free dictionary online, we get the following definition of a gene: ‘The basic physical unit of heredity; a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for the synthesis of RNA, which, when translated into protein, leads to the expression of hereditary character.’ But Mendel had no notion of genes as such, and he certainly knew nothing about DNA. His discoveries languished in some little-read papers for forty years before they were rediscovered and their importance was more fully understood. But in time his idea about the discrete packets of heredity we now call genes helped to answer a very important medical mystery: how certain diseases come about through an aberration of heredity.
We now know that genes are the basic building blocks of heredity in much the same way that atoms are the physical units that make up the physical world. But during the early decades of the twentieth century, nobody had any real notion of what genes were made from, or how they worked. But here and there, people began to study genes in more depth by examining their physical expression during the formation of embryos or in the causation of hereditary diseases. Fruit flies became the experimental model for pioneering research in the laboratory of Chicago-based geneticist Thomas Hunt Morgan, where researchers located genes, one by one, onto structures called chromosomes, which were themselves located within the nuclei of the insect’s germ cells. The botanical geneticist Barbara McClintock confirmed that this was also the case for plants. McClintock developed techniques that allowed biologists to visualise the actual chromosomes in maize, leading to the groundbreaking discovery that, during the formation of the male and female germ cells, the matching, or ‘homologous’, chromosomes from the two parents lined up opposite each other and then the chromosomes swapped similar bits so that the offspring inherited a jumbled-up mixture of the inheritance from the two parents. This curious genetic behaviour (which is known as ‘homologous sexual recombination’) is the explanation of why siblings are different from one another.
By the early 1930s biologists and medical researchers knew that genes were actual physical entities – chemical blocks of information that were lined up like beads in a necklace along the lengths of chromosomes. In other words, the genome could be loosely compared to a library of chemical information in which the books were the chromosomes. The discrete entities known as genes could then be compared to discrete words in the books. The libraries were housed in the nuclei of the germ cells – in human terms, the ova and sperm. Humans had a total stack of 46 books, which were the summed complement of ova and sperm, in every living cell. This came about because the germ cells – the ovum and the sperm – contained 23 chromosomes, so that when a human baby was conceived the two sets of the parental chromosomes united within the fertilised ovum, passing on the full complement of 46 chromosomes to the offspring. But this initial unravelling of the ‘heredity mystery’ merely opened up a Pandora’s box of new mysteries when it came to applying genetics to the huge diversity of life on our fecund planet.
For example, did every life form, from worms to eagles, from the protozoa that crawled about in the scum of ponds to humanity itself, carry the same kinds of genes in their nuclei-bound chromosomes?
The microscopic cellular life forms, including bacteria and archaea, do not store their heredity in a nucleus. These are called the ‘prokaryotes’, which means pre-nucleates. All other life forms store their heredity in nuclei and are known collectively as ‘eukaryotes’, which means true nucleates. From the growing discoveries in fruit flies, plants and medical sciences, it was becoming rather likely – excitingly so – that some profound commonalities might be found in all nucleated life forms. But did the same genetic concepts, such as genes, apply to the prokaryotes, which reproduced asexually by budding, without the need for germ cells? At this time within the world of early bacteriology there was even a debate as to whether bacteria should be seen as life forms at all. And viruses, which were for the most part several orders of magnitude smaller than bacteria, were little understood.
Over time many researchers came to see bacteria as living organisms, classifying them according to the binomial Linnaean system; so, for example, the tuberculosis germ was labelled Mycobacterium tuberculosis and the boil-causing coccoid germ was labelled Staphylococcus aureus. Oswald Avery, with his extremely conservative nature, kept his options open, eschewing the binomial system and referring to the TB germ as the ‘tubercle bacillus’. It is instructive for our story that Dubos, who came to know Avery better than any other colleague, would observe that ‘Fess’ was similarly conservative in his approach to laboratory research. Science must adhere with a puritanical stringency to what can be logically observed and definitively proven in the laboratory.
In 1882 German physician Robert Koch discovered that Mycobacterium tuberculosis was the cause of the greatest infectious killer in human history – tuberculosis. Koch constructed a code of logic that would be applied to bugs when first determining if they caused specific diseases. Known as ‘Koch’s postulates’, this was universally adhered to, and once a causative bug had been identified it was studied further under the microscope. Thus the bug was duly classified in a number of ways. If its cells were rounded in shape it was a ‘coccus’, if a sausage shape it was a ‘bacillus’, if a spiral shape it was a ‘spirochaete’. Bacteriologists methodically studied the sort of culture media in which a bug would grow best – whether in agar alone, or agar with added ox blood, and so on. They also studied the appearance of the bacterial colonies when they were grown in culture plates – their colours, the size of the colonies, whether they were rough in outline or round and smooth, raised or flat, stellate, granular or daisy-head. So the textbooks of bacteriology extended their knowledge base on a foundation of precise factual study and observation. And as understanding grew, this newfound knowledge was applied to the war against infection.
One of the useful things they learnt about disease-causing, or ‘pathogenic’, bacteria was that the behaviour of the disease, and thus of the bug itself in relation to its infected host, could be altered by various deliberate means: for example, through repeated cultures in the laboratory, or by repeatedly passing generations of the bug through a series of experimental animals. Through such manipulations it was possible to make the disease worse or less severe by making the bug either ‘more virulent’ or ‘attenuated’. Bacteriologists looked for ways to extrapolate this to medicine. In France, for example, the eminent Louis Pasteur used this principle of attenuation to develop the first vaccine to be used successfully against the otherwise universally fatal virus infection of rabies.
One fascinating observation that came out of these studies was the fact that, once a bug had been attenuated or been driven to greater virulence, the change in behaviour could be ‘passed on’ to future generations. Could it be that some factor of the bug’s own heredity had been altered to explain the change in behaviour?
Bacteriologists talked about ‘adaptation’, using the same term that was coming into vogue with evolutionary biologists when referring to evolutionary change in living organisms as they adapted to their ecology over time. While it was too early to be sure if bacterial heredity depended on genes, these scientists linked it to the physical appearance of bugs and colonies, or to the bugs’ internal chemistry, and even to their behaviour in relation to their hosts. These were measurable properties, the bacterial equivalents of what evolutionary biologists were calling the ‘phenotype’ – the physical make-up of an organism as opposed to what was determined by the hereditary make-up, or ‘genotype’.
Bacteriologists also came to recognise that the same bacterium could exist in different subtypes, which could often be distinguished from one another using antibodies. These subtypes were called ‘serotypes’. In 1921 a British bacteriologist, J. A. Arkwright, noticed that the colonies of a virulent type of dysentery bug, called Shigella, growing on the jelly-coated surfaces of culture plates, were dome-shaped with a smooth surface, whereas colonies of an attenuated, non-virulent, type of dysentery bug were irregular, rough-looking and much flatter. He introduced the terms ‘Smooth’ and ‘Rough’ (abbreviated to S and R) to describe these colonial characteristics. Arkwright recognised that the ‘R’ forms cropped up in cultures grown under artificial conditions, but not in circumstances where bacteria were taken from infected human tissues. He concluded that what he was observing was a form of Darwinian evolution at work.
In his words: ‘The human body infected with dysentery may be considered a selective environment which keeps such pathogenic bacteria in the forms in which they are usually encountered.’
Soon researchers in different countries confirmed that loss of virulence in a number of pathogenic bacteria was accompanied by the same change in colony appearance from Smooth to Rough. In 1923, Frederick Griffith, an epidemiologist working for the Ministry of Health in London, reported that pneumococci – the bugs that caused epidemic pneumonia and meningitis which were of particular interest to Oswald Avery at the Rockefeller Laboratory – formed similar patterns of S and R forms on culture plates. Griffith was known to be a diligent scientist and Avery was naturally intrigued.
Griffith’s experiments also produced an additional finding, one that really shook and puzzled Avery.
When Griffith injected non-virulent R-type pneumococci from the strain known as type I into experimental mice, he included an additional ingredient in the injections, a so-called ‘adjuvant’, which usually pepped up the immune response to the R pneumococci. A common adjuvant for these purposes was mucus taken from the lining of the experimental animal stomach. But for some obscure reason Griffith switched adjuvant to a suspension of S pneumococci, derived from type II, that had been deliberately killed off by heat. The experimental mice died from overwhelming infection. In the blood of these dead mice Griffith expected to find large numbers of multiplying R-type I bacteria – the type that he had injected at the start of the experiment. Why then had he actually found S-type II? How on earth could adding dead bacteria to his inoculum have changed the actual serotype of the bacterium from non-virulent R-type I to highly virulent S-type II?
Researchers, including Avery himself, had previously shown that S and R types were determined by differences in the polysaccharide capsules coating the cell bodies of the bugs. Griffith’s findings suggested that the test bacteria, initially R-type pneumococci, had changed their polysaccharide coats inside the infected bodies of the mice to that of the virulent strain. But they could not have achieved this by just flinging off the old coat and putting on the new one. The coat was determined by the bacteria’s heredity – it was an inherited characteristic. Further cultures of the recovered bacteria confirmed that the S type bred true. There appeared to be only one possible explanation: adding the dead S bacteria to the living R bacteria had induced a mutation in the heredity of the living R-type bacteria, so they literally transformed into S-type II.
In the words of Dubos: ‘[At the time] Griffith took it for granted that the changes remained within the limits of the species. He probably had not envisaged that one pneumococcus type could be transformed into another, as this was then regarded as the equivalent of transforming one species into another – a phenomenon never previously observed.’
*
It is little wonder that Avery was astonished by Griffith’s findings. Like Robert Koch before him, Avery subscribed to the view that bacterial strains were immutable in terms of their heredity. The very concept of a mutation – that heredity was capable of an experimentally induced change – was a highly controversial issue within biology and medicine at this time. To understand why, we need to grasp the concept of what a mutation means.
By the late nineteenth century Darwinian theory had entered a crisis. Darwin himself had been well aware that natural selection relied on some additional mechanism, or mechanisms, capable of changing heredity, so that natural selection would have a range of ‘hereditable variation’ to choose between. Generations later, in the opening chapters of his innovative book Evolution: The Modern Synthesis,Julian Huxley put his finger on the nub of the problem. ‘The really important criticisms have fallen upon Natural Selection as an evolutionary principle and centred round the nature of inheritable variation.’ In 1900, a Dutch biologist, Hugo de Vries, put forward a novel mechanism that would be capable of providing the necessary variation: the concept of a random change in a unit of inheritance. Opportunity for change exists when genes are copied during reproduction, when a random change in the coding of a gene might arise from an error in copying the hereditary information. De Vries called this source of hereditary change a ‘mutation’. It was only with what Julian Huxley termed ‘the synthesis’ of Mendelian genetics – the potential for change in the inherited genes through mutation – and Darwinian natural selection operating on the hereditary choices presented within a species, that Darwinian theory became credible again to the great majority of scientists.
In time Griffith’s finding would be confirmed to be what Avery was now wondering about: it was a mutation. Geneticists would show that the change from the R to the S strain of pneumococcus involved the transfer of a gene from the dead S-type II bacteria to the living R-type I bacteria, which was incorporated into subsequent bacterial reproductive cycles, transforming the cells of the R-type I bacterium into the cells of the S-type II bacterium. It was indeed the bacterial equivalent of a change of species. And Griffith was proven right in inferring that Darwinian natural selection had operated even in the short time frame of the infection of a cohort of laboratory mice.
Griffith’s experimental findings galvanised bacteriologists and immunologists around the world. His discovery was confirmed in several different research centres, including the Robert Koch Institute in Berlin, where the pneumococcal types had first been classified. The news was inevitably a hot topic of discussion in Avery’s department, as Dubos would recount: ‘but we did not even try to repeat them at first, as if we had been stunned and almost paralysed intellectually by the shocking nature of the findings’.
At first Avery simply couldn’t believe that bacterial types could be transformed. Indeed, he had been one of the authoritative figures who had settled the fixity of bacterial reproduction being true to type years before. But from 1926 Avery encouraged a young Canadian physician working in the Rockefeller Laboratory, M. H. Dawson, to investigate the situation. According to Dubos, Dawson, unlike Avery, was convinced from the start that Griffith’s conclusion must be correct because he believed that ‘work done in the British Ministry of Health had to be right’.
Dawson began by confirming Griffith’s findings in laboratory mice. His results suggested that the majority of non-virulent bacteria – the R types – had the ability in certain circumstances to revert to the virulent S type. By 1930 the young Canadian was joined by a Chinese colleague, Richard P. Sia, and between them they took the experimental observations further by confirming that the hereditary transformation could be brought about in culture media, without the need for passage through mice. At this stage, Dawson left the department and Avery encouraged another young physician, J. L. Alloway, to take the investigation further. Alloway discovered that all he needed to bring about the transformation was a soluble fraction derived from the S pneumococci by dissolving the living cells in sodium deoxycholate, then passing the resultant solution through filters to remove the bits of broken-up cells. When he added alcohol to the filtered solution, the active material precipitated out as sticky syrup. Throughout the laboratory this sticky syrup was referred to as the ‘transforming principle’. So the work continued, experiment following experiment, year by year.
When Alloway left the department, in 1932, Avery began to devote some of his own time to the pneumococcus transformation, in particular aiming to improve the extraction and preparation of the transforming substance. Frustration followed frustration. He focused on its chemical nature. Discussion took place with other members of the department, ranging from the ‘plamagene’ that was thought to induce cancer in chickens (now known to be a retrovirus), or to the genetic alterations in bacteria that were thought to be caused by viruses. According to Dubos, Alloway suggested the transforming agent might be a protein-polysaccharide complex. But by 1935 Avery was beginning to think along other lines. In his annual departmental report that year he indicated that he had obtained the transforming material in a form that was essentially clear of any capsular polysaccharide. In 1936, Rollin Hotchkiss, a biochemist who had now arrived to work in the department, wrote a historic comment in his personal notes:
‘Avery outlined to me that the transforming agent could hardly be a carbohydrate, did not match very well with a protein and wistfully suggested it might be a nucleic acid!’ At this stage, Dubos, who many years later would write a book about Avery and his work, dismissed this as no more than a surmise. There were good reasons for his caution.
That year few researchers throughout the world believed that the answer to heredity lay with nucleic acids. These chemical entities had been discovered by a Swiss biochemist, Johann Friedrich Miescher, back in the late 1800s. Fascinated by the chemistry of the nucleus, Miescher had broken open the nuclei of white blood cells in pus, and subsequently the heads of salmon sperm, to discover a new chemical compound which was acidic to pH testing, rich in phosphorus and comprised of enormously large molecules. After a lifetime of experimentation on the discovery, Miescher’s pupil, Richard Altmann, would introduce the term nucleic acid to describe Miescher’s discovery. By the 1920s, biochemists and geneticists were aware that there were two kinds of nucleic acids. One was called ribonucleic acid, or RNA, which contained four structural chemicals: guanine, adenine, cytosine and uracil, or GACU. The other was called ‘desoxyribonucleic acid’, or DNA, which was a major component of the chromosomes. They had deciphered its four bases – three identical to RNA, guanine, adenine and cytosine, but with the uracil replaced by thymine – making the acronym GACT. They knew that these four bases consisted of two different pairs of organic chemicals; adenine and guanine being purines, and cytosine and thymine being pyrimidines. They also knew that they were strung together to form very long molecules. At first they thought that RNA was confined to plants while DNA was confined to animals, but by the early thirties this was dismissed when it was found that both RNA and DNA were universally distributed throughout the animal and plant kingdoms. Still they had no knowledge of what nucleic acids actually did in the nuclei of cells.
A distinguished organic chemist based at the Rockefeller Institute, Phoebus Aaron Levene, proposed that the structures of DNA and RNA were exceedingly boring – they formed groups of four bases that repeated themselves in the identical repetitive formation throughout the molecule, like a four-letter word, repeated ad nauseam. This was called ‘the tetranucleotide hypothesis’. Such a banal molecule couldn’t possibly underlie the exceedingly complex basis of heredity. In the words of Horace Freeland Judson, ‘the belief was held with dogmatic tenacity that DNA could only be some sort of structural stiffening, the laundry cardboard in the shirt, the wooden stretcher behind the Rembrandt, since the genetic material would have to be protein’.
Proteins are lengthy molecules made up of smaller organic chemical units known as amino acids. There are 20 amino acids in the make-up of proteins, reminiscent of the number of letters that make up alphabets. If genes were the hereditary equivalents of words, only the complexity of proteins could fashion the words capable of spelling out the narratives. Chemists, and through extrapolation geneticists, not unnaturally assumed that only this level of complexity could possibly accommodate the incredible memory template that the complexity of heredity demanded – a line of thought that Judson labelled ‘The Protein Version of the Central Dogma’.
This was the contentious zeitgeist that Avery now confronted. As early as 1935, in his annual reports to the Board of the Institute, he indicated that he had growing evidence that the ‘transforming substance’ appeared free of capsular polysaccharide and it did not appear to be a protein.
Further progress on this line of research appeared to drag. In part this was because Dubos, working in the same department, had made a breakthrough in his search for antibiotic drugs. In 1925, Alexander Fleming, at St Mary’s Hospital in London, had discovered a potential antibiotic, penicillin, but he had been unable to take his work to the stage of useful production for medical purposes. Now, working on the philosophical principle encapsulated by the biblical saying ‘dust to dust’, Dubos had pioneered the search for microbes in soil that would potentially attack the polysaccharide coat of the pneumococcus. By the early 1930s he was making progress. From a cranberry bog in New Jersey he found a bacillus that dissolved the thick polysaccharide capsule that coated the pneumococcus with its armour-like outer covering. Dubos went on to extract the enzyme that the Cranberry Bog bacillus produced. He and Avery had reported their discovery in a paper in the journal, Science, in 1930. In a further series of papers the two scientists would report further experiments, all aimed at extrapolating the discovery to human trials of the Cranberry Bog enzyme in treating the potentially fatal pneumonia and meningitis caused by the pneumococcus.
But their researches encountered difficulty after difficulty. In part these arose from a predictable ignorance in a field of such pioneering research. A more personal, and devastating, problem arose when, under the stress of it all, Avery developed thyrotoxicosis – a debilitating autoimmune illness in which his thyroid gland became overactive.
Thyrotoxicosis causes the system to be flooded by thyroid hormones, which would have inappropriately switched his metabolism into a dangerous overdrive. He would have felt shaky, agitated, physically and mentally restless, suffering difficulties with relaxation and sleep – an impossible situation for a creative person. Avery had to spend time away from the lab undergoing surgery to remove the bulk of the ‘toxic goitre’, a procedure that carried risk of side-effects, even fatality in a minority of cases. His surgeon advised him against any early activity, physical or mental, that provoked stress. Dubos later recalled how Avery was away from his work for as long as six months. And while Avery was away, the laboratory stagnated. In Dubos’ own words, ‘I … pursued [the research] for three or four years. However I could not carry the work very far because there were serious gaps in both my knowledge of genetics and biochemistry and in the [prevailing] states of these sciences themselves.’
Dubos would continue his researches against such difficulties, to be rewarded, in 1939, with the discovery of the first soil-derived antibiotic. He called it ‘gramicidin’. But gramicidin could not be taken by mouth or administered by injection because it was too toxic. It could only be applied to skin conditions. The research continued. But then, all of a sudden, the hopes of Avery and Dubos were overtaken by a rival breakthrough. Working in the pharmaceutical research laboratories of the Bayer Company in Elberfeld, Germany, doctor Gerhard Domagk reported the discovery of a new antibacterial agent called prontosil. The first of what would come to be known as the sulphonamide drugs, it immediately entered the medical formulary, pioneering the treatment of a number of hitherto untreatable infectious diseases.
Today we are apt to forget how little we could do to control infection in the 1930s. Epidemics such as scarlet fever, measles, pneumonia, meningitis and poliomyelitis swept through the population in regular, sometimes annual, cycles. Other notorious infections were everyday threats, including tuberculosis, which ravaged entire families, or boils, septic arthritis, septic osteomyelitis, which caused agonising abscesses in bone, and the commonplace but potentially deadly streptococci capable of breaking through a septic throat to cause abscesses in the brain. Most of the human population, whether in developed or developing countries, died from infections, including the insidious pneumonias that hit those whose immunity was depressed. The treatment of infections was the most urgent problem then facing humanity. For Dubos, and even more so Avery, the disappointment of failing in their line of research would have been shattering.
When, in due course, Avery returned to work, he switched the emphasis of his research to the ‘transforming substance’. Colin MacLeod improved the techniques of extraction so they could now produce sizeable amounts for assay and further testing. They began to make more rapid progress so that, in a report to the Rockefeller Board for the year 1940–41, they were more confident in stating that even a highly purified extract of the transforming substance appeared to be protein-free.
That summer MacLeod left the Institute to become Professor of Bacteriology at the New York University School of Medicine. But he still took an interest in the project and frequently returned to the Institute to add his advice. A young paediatrician, Maclyn McCarty, took MacLeod’s place in the transforming experiment. McCarty brought a useful level of biochemical training to the laboratory. And now they had the transforming substance in quantity and in stable form, he applied his chemical skills to further process and identify the active material. He began to culture the pneumococci in large batches of 50 to 75 litres, developing a series of steps that increased the yield of transforming substance while removing proteins, polysaccharides and ribonucleic acid. The prevailing beliefs about the hereditary principle claimed that nucleoproteins were the answer. Thus the topmost priority in all of this effort was to ensure that the final test material contained no protein.
By now McCarty had extracted concentrated solutions of the active material. He treated this with a series of protein-digesting enzymes, such as the gut-derived trypsin and chymotrypsin, which were known to destroy proteins, ribonucleic acid and pneumococcal capsular polysaccharide. What remained was once more shaken with chloroform in a final effort to remove even the finest traces of protein.
By late 1942, after repeated extraction and experiment, McCarty had come to the conclusion that the transforming activity was confined to a highly viscous fraction that consisted almost exclusively of polymerised deoxyribonucleic acid. When he precipitated this fraction in a flask by adding absolute ethyl alcohol, drop by drop, all the while stirring the solution with a glass rod, the active material separated out of the solution in the form of long, white and extremely fine fibrous strands that wound themselves around the stirring rod. Dubos would recall the excitement felt within the lab by all those who witnessed the sight of the beautiful fibres, which were the pure form of the transforming substance.
In early 1943, Avery, MacLeod and McCarty presented their findings to distinguished chemists at the Princeton section of the Rockefeller Institute for Medical Research. The chemists must have been astonished, perhaps even nonplussed, but they offered no contradiction of the evidence nor asked for further proof. The researchers summed up the evidence for the Board of the Rockefeller in April of that year. Avery, MacLeod and McCarty, all three medical doctors rather than geneticists, were now ready to inform the world in a paper submitted to the Journal of Experimental Medicine in November the same year, which would be published early the following year. The title of the paper was long-winded and cautious: ‘Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Induction of transformation by a desoxyribonucleic acid fraction isolated from pneumococcus type III’.
In the words of Dubos, this paper ‘had staggering implications’. The sense of excitement, tempered by caution, was captured in a letter that Avery wrote to his brother, Roy, dated 26 May 1943:
… For the past two years, first with MacLeod and now with Dr McCarty, I have been trying to find out what is the chemical nature of the substance in the bacterial extracts which induces this specific change … Some job – and full of heartaches and heartbreaks. But at last perhaps we have it … In short, the substance … conforms very closely to the theoretical values of pure desoxyribose nucleic acid. Who could have guessed it?
In the letter, ‘desoxyribose nucleic acid’, in the paper, ‘desoxyribonucleic acid’: these are older names for what we now call deoxyribonucleic acid – commonly reduced to its acronym, DNA.
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DNA Is Confirmed as the Code (#ulink_a8f9dc67-6bfa-5215-bbf6-a95d6a68aef6)
Looking back at his own failure to appreciate Avery’s discovery at the time, Stent came to the conclusion ‘in some respects Avery et al’s paper is a more dramatic example of prematurity than Mendel’s’.
UTI DEICHMANN
Scientists, in the opinion of the Nobel Prize-winning Linus Pauling, were fortunate because their world was so much the richer for its mysteries than those not interested in science could possibly appreciate. Certainly in those days Avery’s lab at the Rockefeller Medical Institute for Research was filled with a mood of expectation and excitement. In 1943 Oswald Avery was 65 years old. He had planned to retire and join his brother Roy’s family in Nashville, Tennessee, but there was no question of his leaving the lab at this time. He needed to continue his work on the transforming substance. In particular he needed to convince his colleagues throughout the world of microbiology and, more widely, the sceptical world of biochemists and geneticists, of the validity of their discovery.
Avery was conservative by nature. A generation earlier he and a colleague had proposed that complex sugar molecules, called polysaccharides, and not proteins determined the immunological differences between different types of pneumococcal bacteria. Although this theory was eventually confirmed to be true, at the time of discovery it provoked a storm of controversy that had haunted this nervous and sensitive man. In a long and rambling letter to his brother Avery had repeatedly referred to his worry about the reaction to the new discovery. ‘It’s hazardous to go off half-cocked … It’s lots of fun to blow bubbles – but it’s wiser to prick them yourself before someone else tries to.’
Avery had an adversary closer to home. Alfred E. Mirsky, a distinguished biochemist and geneticist also working at the Rockefeller Institute, had reacted to Avery’s discovery with incredulity. To make matters worse, Mirsky was widely regarded as an expert on DNA. He had discovered that the quantity of DNA in every cell nucleus remained the same, establishing a principle called ‘DNA constancy’. He now doubted the efficacy of McCarty’s DNA extraction. A stickler for ‘clean’ biochemical experiment, Mirsky believed that protein found in the nucleus, called nucleoprotein, must be the basis of heredity. Even as late as 1946, Mirsky insisted that the two enzymes McCarty had used in his extractions would not digest away all of the protein. Mirsky was very influential in genetic circles and his argument impressed the leading geneticist of the time, Hermann J. Muller, who had been awarded the Nobel Prize that same year for his discovery, made two decades earlier, that X-rays caused mutations in the genes of the fruit fly. In a letter to a geneticist colleague, Muller stated ‘Avery’s so-called nucleic acid is probably nucleoprotein after all, with the protein too tightly bound to be detected by ordinary method.’
To some extent such disagreement was typical of the situation one might find anywhere in science when various groups from different scientific backgrounds are investigating a major unknown. Never is the argument more acrimonious than when a new discovery confounds the accepted paradigm. But the vociferous opposition of Mirsky from within Avery’s home research foundation must have been particularly damaging. In 1947 Muller published his ‘Pilgrim’s Lecture’ as a scientific paper in which he concluded that whether nucleic acid or protein was the answer ‘must as yet be regarded as an open question’. In the words of Robert Olby, a historian and philosopher of science, ‘Through Muller’s widely read Pilgrim Lecture, this [sceptical] influence was spread to a wide audience.’
In a new series of extractions, with stringent quality checking, Avery attempted to confound his critics. McCarty left the laboratory in 1946, which was left in the hands of, amongst others, the meticulous Rollin Hotchkiss. Hotchkiss added several new chemical explorations of the extract, all further confirming that it was DNA. He disproved Mirsky’s objection by purifying the extract to the extent that the protein content was below 0.02 per cent and he showed that it was inactivated by a newly discovered crystalline enzyme specific to DNA: DNase. While many geneticists remained obdurate in their opposition, some were beginning to take notice.
In a subsequent interview with the biophysicist and future Nobel Laureate, the German-born physicist Max Delbrück, Horace F. Judson would discover that some distinguished researchers were aware of the potential importance of Avery’s discovery. ‘Certainly there was scepticism,’ Delbrück recalled. ‘Everybody who looked at it was confronted by this paradox. It was believed that DNA was a stupid substance … which couldn’t do anything specific. So one of these premises had to be wrong. Either DNA was not a stupid molecule, or the thing that did the transformation was not DNA.’ Avery had raised a monumentally important question and the only way of resolving the dilemma was for other researchers to probe it through some form of alternative experimentation to find out if he was right or wrong.
In 1951, two American microbiologists, Alfred Hershey and Martha Chase, undertook such an alternative experiment while studying the way that certain viruses use bacteria as a factory to make daughter viruses. These viruses are called ‘bacteriophages’, or ‘phages’ for short – from the Greek phago, which means to eat, because they devour cultures of host bacteria. The presence, and number, of viruses could be measured if you seeded your host bacteria into heat-softened agar and then added the viruses in various dilutions to the agar before spreading it over a laboratory plate. When the agar cooled it formed a thin, even layer of jelly in the plate, which, on overnight culture, would become clouded by growth of bacteria within the agar. Wherever a virus landed among the bacteria there would be a round window of transparency caused by the dissolving (lysis) of the bacteria which was easily visible, and thus countable. This ‘plaque-counting technique’, which I myself learnt from my microbiology professor as a medical student and later made use of in experiments on the nature of autoimmunity as a hospital doctor, is easily learnt and thus put to use by thousands of scientists in a great variety of experiments.
What interested Hershey and Chase was the fact that phage viruses were known to compose a core of genetic material surrounded by a capsule of protein. In fact, each virus closely resembled a medical syringe in structure, so that when it infected the bacterial cell of its host, it appeared to squeeze out the genetic material from the body of the syringe, leaving the empty protein coat attached to the outer bacterial cell wall. Meanwhile, the genetic material was injected into the bacterial cell interior, where the viral genome would be replicated as part of its reproduction. Hershey and Chase invented an ingenious experiment that would decide whether protein or DNA was the basis of the viral reproductive system. This would involve adding radioactive phosphorus and radioactive sulphur to the media in which separate batches of the host bacteria were growing. After four hours, to allow the radioactive element to be taken up by the bacteria, they introduced the phage viruses.
To understand the basis of the experiment we need to grasp that DNA contains phosphorus as part of its make-up but no sulphur, meanwhile the amino acids that make up proteins contain sulphur but no phosphorus.
By inoculating each of these two groups of bacteria with viruses, Hershey and Chase derived two populations of phage viruses – one containing the radioactive phosphorus and the other containing the radioactive sulphur. When the viruses infected the bacteria, they left their empty viral coats, mostly made up of protein, attached to the outside of the bacterial cell walls, having injected their core material, known to comprise DNA, into the bacterial bodies. Hershey and Chase used centrifugation to separate and extract empty viral coats. Meanwhile, the infected bacteria were allowed to go through their normal reproductive cycle, which allowed the viral cores inside them to generate entire new phage viruses, rupturing the bacterial bodies and flooding the growth media with large numbers of fully formed viruses. Hershey and Chase now removed what was left of the host bacterial bodies to gather dense concentrations of fully formed viruses.
When they now compared the empty viral coats, made up of protein, with the fully formed viruses, with their cores full of genetic material, they found that 90 per cent of the radioactive sulphur was left behind in the viral coats when the virus infected the cell, and 85 per cent of the phosphorus was now part of DNA that had entered the bacterial cell to code for the future offspring of virus. This confirmed Avery’s findings: DNA, and not protein, was the code of heredity.
We might duly note that this separation of coat from core DNA of virus involves a much higher degree of protein impurity than Avery’s extractions. Yet the hitherto sceptical geneticists appeared to be more convinced by the phage experiment than by Avery’s work. Perhaps the strikingly visual nature of the experiment was a factor. Perhaps it was the additional, quite different, avenue of confirmation. It didn’t harm credibility that leading geneticists were within the ‘phage camp’, too.
*
Today, with the advantage of retrospect, scientists by and large see the 1944 paper by Avery, MacLeod and McCarty as the pioneering discovery of DNA as the molecule of heredity. It has been portrayed as one of the most regrettable examples of a discovery that merited, but was not awarded, the Nobel Prize. There is ample evidence that Avery was recommended by senior colleagues, particularly within his own discipline of microbiology and immunology – indeed he was nominated twice, first in the late 1930s, for his work on the pneumococcal typing and its relevance to bacterial classification, and, after the 1944 paper was published, he was nominated yet again for his fundamental contribution to biology. But it would appear that the Nobel Committee was not sufficiently swayed. In retrospect, it is seen as a major omission that causes people to scratch their heads and wonder why.
Dubos worked for fifteen years in the lab next door to Avery’s and, in so much as the reticent Professor allowed it, he had plenty of opportunity to get to know Avery and to understand his approach to science and his reaction to the stresses involved in pioneering new concepts. In Dubos’ opinion, writing in 1976, the curious lack of recognition most likely derived from a combination of happenstance and Avery’s own personality. He would subsequently remark how, in all that time, Avery never closed the door of his lab, or the small office that led off it, allowing any of his staff to come and talk to him. This same eternally open door also allowed Dubos to witness ‘Fess’s’ activities at the bench, to listen in to his conversations with colleagues and to observe his interludes of introspective brooding.
This reserved, small and slender bachelor would inevitably arrive at work dressed in a neat and subdued style, his conservative attire somehow at one with the charm of his lively and affable behaviour. His eyes, under the domed bald head that seemed too voluminous for the frail body, were sparkling and always questioning, and he would transform the most ordinary conversation into an artistic performance with spirited gestures, mimicry, pithy remarks and verbal pyrotechnics. Avery might have been somewhat reticent in manner (he could be silently introspective), but in his own quintessential way he was vulnerably human, and that made him all the more interesting and enchanting.
I would suggest that creativity in science is every bit as intertwined with personality as one finds in a writer, artist, or musically gifted composer or performer. It would seem unsurprising in an artist if he appeared unusually ascetic, withdrawn from the hurly-burly world of the surrounding New York, ensuring that he lived close enough to the Rockefeller Institute so he could walk to work. In his ways, Avery could seem curiously ambivalent. He suffered mood swings at times, when alone in the lab, when he would appear to be dejected by the difficulties facing him. Afterwards he would declaim, clearly referring to himself, that resentment hurts the person who resents much more than the person who is resented. He left many letters unanswered and refused to have a secretary. He refused to review, or sponsor, any scientific paper in which he had made no contribution. In Dubos’ words, ‘Graciousness and toughness when it came to what he himself was determined to do, was part of his nature.’ Avery was a very successful teacher during his early medical career, yet in his later years he appears to have resented being expected to lecture on his own research. In this respect, he bore some interesting similarities to Charles Darwin. Avery scrupulously avoided any discussion of his own health and any intrusion, however small, into his private life – which was devoted to his younger brother, Roy, and to an orphaned first cousin whom he supported all through his life. He never expressed resentment about criticisms of his work, even when these were unjustified. He left no record of his private thoughts, other than the letters to his brother. A single experience struck Dubos as being significant.
One day, in early 1934, the same year that Avery suffered the onset of his thyrotoxicosis, Dubos told Avery that he was about to be married. The lady in question was a Frenchwoman living in New York, named Marie Louise Bonnet. Avery immediately rejoiced at the news. They were conversing in the laboratory on the sixth floor of the Rockefeller hospital building. During the subsequent animated conversation, Avery climbed out of his chair, walked to the window and looked out, as if lost for a moment in deep reflection. Returning to his chair, he mentioned that he had contemplated marriage years before, but that circumstances had not proved favourable to his plans. It seems likely that the lady in question was a nurse that Avery had met during the course he had taught to student nurses at the Hoagland Laboratory. Avery would have been about 32 years old at the time. For a moment or two the older man’s eyes were full of longing.
‘One of the great joys of life,’ he remarked to Dubos, ‘is to go home to someone who would rather see you than anybody else.’
Fate would prove cruel to both men. Marie Louise Bonnet subsequently died from tuberculosis at a time when Dubos was pioneering the very antibiotics that would eventually help to cure the same illness. The marriage was childless and the effects of his wife’s death on Dubos were devastating. He resigned, forthwith, from his antibiotic researches, which were later taken up by his former teacher, Selman Waksman at Rutgers Agricultural College, now Rutgers University, and which led to the discovery of a series of important antibiotics, including streptomycin. This breakthrough resulted in Waksman being awarded the Nobel Prize in Medicine or Physiology in 1952.
Much of what Dubos witnessed of Avery spoke of an intense focus and purity of purpose in science and his work. But, increasingly, his devotion to his research appeared to be accompanied by insularity bordering on reclusiveness.
Scientists who have laboured long and hard at a difficult but eventually rewarding line of research are usually happy to talk about it – if not to the media or ordinary social channels, certainly to colleagues. They travel to scientific symposia. They take part in conferences. They enjoy the camaraderie that comes from sharing the same interests. In the words of Frank Portugal, ‘wide-ranging discussions with peers both individually and at meetings are part and parcel of the scientific process. It is an important component of how collaborations are formed and scientific advances are made and respected.’ Most scientists are only too glad to accept the, often rare, honours and distinction their work brings their way. Not so Oswald Avery.
In 1944 Avery was proposed for an honorary degree at Cambridge University, a recognition most scientists would cherish. The following year he was awarded the Copley Medal by the Royal Society of London. Avery’s roots were English – in the late nineteenth century his family had emigrated to Canada from the city of Norwich – but he refused to visit England even on such prestigious occasions, putting forward the excuse that his state of health did not permit it except by travelling first class. In Dubos’ opinion, this was disingenuous, since the respective foundations would have funded the flights. That he might have felt nervous, claustrophobic, on the lengthy flight is possible. Recalling those dark moods in which Avery might mumble to himself about the damaging inflictions of resentment, it seemed more than likely to Dubos that he might have been unable to suppress lingering anger at the hurtful controversy provoked years ago by his polysaccharide typing of pneumococci. Whatever his reasons, Avery refused both honours.
An incident highlighted just how strong was Avery’s aversion to such formal acknowledgement of his work. Sir Henry Dale, who was President of the Royal Society in England, took it upon himself to bring the Copley Medal to the Rockefeller Institute, there to confer it on the shy and retiring Avery in person. Dale was accompanied by a Dr Todd, who knew Avery personally. The two highly respected English visitors arrived at the Institute in New York unannounced and went directly to Avery’s department in the main hospital building. But when they saw Avery working in his lab, through the ever-open door, they retreated without intruding on his presence.
Dr Todd would later recount how Sir Henry Dale said simply: ‘Now I understand everything.’
Bizarre as this behaviour would appear, it was in keeping with Avery’s increasingly reclusive personality: a man who avoided any of the normal personal contacts outside of immediate family and work colleagues. Genius can be strange. Yet such idiosyncratic behaviour apart, it was this son of an evangelical Baptist preacher who first discovered that DNA was the molecule of heredity. And putting such personal matters aside, the question remains: why was such a fundamental discovery not recognised by the awarding of the Nobel Prize?
In his letters to his brother, Avery retained a modest outlook. Could it be that a combination of Avery’s innate conservatism, his tendency to over-caution, and his downplaying of the implications of his discovery in the paper of 1944 might have contributed to his being overlooked? In Dubos’ words, the paper … ‘did not make it obvious that the findings opened the door to a new era of biology’. Dubos wondered if the Nobel Committee, unaccustomed to such restraint and self-criticism ‘bordering on the neurotic’ might have caused them to wait a while for both confirmation of the discovery and to see what the broader implications might be. To put it another way, Dubos questioned if the paper might have been a failure not in its own merits, as a scientific communication, but from the public relations point of view.
This lack of recognition is made all the more puzzling by the fact that, if the importance of the 1944 paper was not universally recognised when it was published, it became more and more obvious with the passage of time. The Hershey and Chase paper was published in 1952. And although he was retired by the time Crick and Watson published their famous discovery of the three-dimensional chemical structure of DNA in 1953, Avery was still alive. He wouldn’t die until two years later, in 1955.
More recently the Nobel authorities have allowed open access to their earlier thinking, and this has confirmed much of what Dubos had concluded. As part of the system for deciding who should get Nobel Prizes, the Nobel Committee receives proposals from leading experts around the world. In the words of Portugal, who reviewed their working and archives, ‘It seems that key biological chemists were not convinced by Avery’s claim that DNA was the basis of heredity.’ Not a single geneticist nominated Avery for the Nobel Prize. In part this may have reflected a difficulty in extrapolating his discovery in a single type of bacterium to genetics more widely, but even those colleagues who did nominate him for the Nobel Prize tended to overlook his work on DNA in favour of his immunological typing of the pneumococcal capsule. Portugal also wondered if Avery’s own idiosyncratic behaviour, including his reluctance to meet with and exchange findings with colleagues, and in particular geneticists, at scientific meetings had unintentionally confounded the acceptance of his groundbreaking discovery.
We are left with a lingering sense of regret that Avery was not accorded the recognition he deserved. He was 67 years old when his iconoclastic paper was published. It was, in the words of the eminent biochemist Erwin Chargaff, the rare instance of an old man making a major scientific discovery. ‘He was a quiet man: and it would have honoured the world more, had it honoured him more.’
But there is a greater acknowledgement of discovery than the awarding of a prize, no matter how respected and prestigious. In the words of Freeland Judson, ‘Avery opened up a new space in biologists’ minds.’ By space he meant he had unravelled a major truth, revealing new unknowns and raising important new questions. Avery himself had, with quintessential modesty, touched upon those important new questions in his letter to his brother:
If we are right, and of course that is not yet proven, then it means that nucleic acids are not merely structurally important but functionally active substances in determining the biochemical activities and specific characteristics of cells – and that by means of a known chemical substance it is possible to induce predictable and hereditary changes in cells. This is something that has long been the dream of geneticists … Sounds like a virus – may be a gene. But with mechanisms I am not now concerned – one step at a time – and the first is, what is the chemical nature of the transforming principle? Someone else can work out the rest …
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The Story in the Picture (#ulink_1f573ad9-98b3-558a-8d1f-470d1b6d5745)
You look at science (or at least talk of it) as some sort of demoralising invention of man, something apart from real life, and which must be cautiously guarded and kept separate from everyday existence. But science and everyday life cannot and should not be separated.
ROSALIND FRANKLIN
The discovery of the ‘transforming substance’ by Avery, MacLeod and McCarty, confirmed by Hershey and Chase’s elegant experiment with the bacteriophage, proved that DNA was the molecule of heredity. But both groups were working with microbes, bacteria and viruses, which were known to be much simpler in their hereditary nature than, say, animals and plants. This left huge unknowns that needed to be explored. Was DNA the key to the heredity of all of life, or was it just relevant to bacteria and viruses? By the early 1950s, work in many different laboratories had confirmed that DNA was a major ingredient in the nuclei of animals and plants. This supported the idea that DNA was the coding molecule of life. But if so, how did it really work? How, for example, did a single chemical molecule code for the complex heredity of a living organism?
Biologists, doctors, molecular biochemists and geneticists were now asking themselves the same, or similar, questions. Critical to any such understanding was the precise molecular structure of DNA. If, for example, we were to regard the role of DNA as akin to a stored genetic memory, how did that molecular structure enable the quality of such a phenomenally complex memory? How was that genetic memory transferred from parents to offspring? How did the same stored memory explain embryological development, where a single cell arising from the genomic union of a paternal sperm and maternal ovum gives rise to the developing human embryo and future adult human being?
There was another profoundly important question.
Darwinian evolution lay at the heart of biology. To put it simply, Darwin’s idea of natural selection implied that nature selected from a range of variations in the heredity of different individuals within a species. The way in which it worked was exceedingly simple, if brutal. Those individuals, and by inference their variant heredities, who carried a small advantage for survival and thus a better chance of giving rise to offspring, would therefore be more likely to contribute to the species gene pool. In reality natural selection worked more through a process of attrition. Those less advantaged individuals who did not carry the advantage for survival, were more likely to perish in the struggle for existence, and thus they were less likely to contribute to the species gene pool.
This is what Darwinian evolutionary biologists refer to as ‘relative fitness’. It is the measure of the individual’s contribution to the species gene pool. Certainly it has nothing to do with racist notions of superiority and inferiority attached to ‘survival of the fittest’ – a term introduced not by Darwin but by the social philosopher Herbert Spencer. But if we take a pause and think about it, such variant heredity, essential for natural selection to work, must also come about through mechanisms involving this wonder molecule, DNA, which must lie not only at the heart of heredity but also at the absolute dead centre of evolution. All of these questions needed to be answered by the scientists now struggling to understand the structure and, assuming structure was function, the properties of this remarkable chemical, DNA.
In fact the first step towards answering these questions had already been taken back in 1943, in what might appear unlikely circumstances. It was taken not by a biochemist, biologist or geneticist, but by an Austrian physicist. The spark was lit when, at 4.30pm on Friday 5 February, Erwin Schrödinger stepped up to the podium in Dublin to deliver a lecture that is now seen as a landmark moment in the history of biology. Schrödinger had been awarded the Nobel Prize in 1933 for work in quantum physics that expanded our understanding of wave mechanics – but I won’t confuse myself or my readers by entering further into the physics. The simple facts were that Schrödinger had exiled himself from his native Austria in protest at human rights abuses and had been given sanctuary in neutral Ireland by its President, Eamon de Valera. In Dublin Schrödinger had helped found the Institute for Advanced Studies. As part of his duties in support of the Institute, he had agreed to give a series of three lectures in which he developed a central theme: ‘What Is Life?’
Such was Schrödinger’s fame that the lecture theatre, which had a seating capacity for 400, could not accommodate all who wished to attend the lectures – this despite the fact that they had been warned in advance that the subject matter was a difficult one and that the lecture was not going to be pitched at an easy or popular level, even though Schrödinger had promised to eschew mathematics. De Valera himself was present in the audience, as were his cabinet ministers and a reporter for Time magazine. One wonders what these politicians and journalists made of Schrödinger’s focus on ‘how the events in space and time which take place within the spatial boundary of a living organism can be accounted for by physics and chemistry’.
Schrödinger subsequently extrapolated the three lectures into a book of less than a hundred pages with the same title: What Is Life? This was published the following year. In what is now a very famous book, Schrödinger popularised a quantum mechanics interpretation of the gene that had been proposed earlier by another distinguished physicist, the previously mentioned Max Delbrück.
In the opening pages of the first chapter, Schrödinger posed the question: ‘How can the events which take place within a living organism be accounted for by physics and chemistry?’ Admitting that at the time of writing the prevailing knowledge within the disciplines of physics and chemistry was inadequate to explain this, he nevertheless hazarded the opinion that ‘the most essential part of a living cell – the chromosome fibre – may suitably be called an aperiodic crystal’. The italicisation is Schrödinger’s to emphasise, as he further explained, that the physics up to this time had only concerned itself with periodic crystals, the kind of repetitive atomic structures seen, for example, in very obvious crystalline compounds such as gemstones.
What did he mean by an ‘aperiodic crystal’?
He explained this with a metaphor. If we examined the images within the pattern of a wallpaper, we could see how the pattern was repeated, over and over. This was the equivalent of a periodic crystal. But if we examined the complex elaboration of a Raphael tapestry, we saw a pattern of images that did not repeat themselves, yet the pattern was coherent and meaningful.
Schrödinger intuited further.
It was the chromosomes, or more likely an axial fibre much finer than what was visible under the microscope, that contained what he termed ‘some kind of code-script’ that determined the blueprint of the individual’s development from fertilised egg to birth – and further determined the functioning of what we would now term the genome throughout the lifetime of the individual.
That intuition would provide the drive for a naïve but highly inquisitive young American, called James Dewey Watson, to join forces with a slightly older but equally inquisitive Englishman, Francis Crick, and form what is now seen as one of the most famous partnerships in scientific history. Both men would take their inspiration from Schrödinger to search for the aperiodic crystal that coded for DNA.
*
Watson was an exceptionally bright child who lived at home with his family in Chicago while attending the local university. He enrolled when aged just 15 and he graduated, aged 19, in 1947 with a bachelor’s degree that included a year studying zoology. His teacher of embryology would remember him as a student who showed little interest in lectures and made no notes whatsoever, so it was all the more puzzling when he graduated top of his class. Watson would subsequently admit to a habitual laziness. Though vaguely interested in birds, he had deliberately avoided any courses that involved chemistry or physics of ‘even medium difficulty’. This self-indulgent student left Chicago with only a rudimentary knowledge of genetics or biochemistry. As part of his education he had attended lectures by the geneticist Sewall Wright, who had devised a mathematical system of studying population genetics. Wright’s course included a discussion of Avery’s work, but Watson would subsequently confess that he took little notice. He would also confess that the inspiration for his subsequent interest in the ‘mystery of the gene’ was Schrödinger’s book, What Is Life?
Inspired by this book, Watson landed a research fellowship at Indiana University, at Bloomington. He was delighted by the move because Nobel Laureate Hermann Joseph Muller was the local Professor of Zoology. As early as 1921 Muller had observed that the genes of the fruit fly underwent mutations – as did the genes of the bacteriophages – the viruses that had inspired Hershey and Chase. Watson was intrigued by the fact that phage viruses could be manipulated in test tubes. Their reproductive cycles were extremely brief – an important consideration for an impatient young scientist. There were simple test systems that could be employed to follow their life cycles, and numbers, in a way that would open up new angles from which to attack the gene problem. All you had to do was carefully design an experiment aimed at probing some particular aspect of the gene problem and the whole shebang could be completed in a matter of days. This intimate, if brutal, interplay between phage viruses and their host bacteria allowed scientists to figure the complex chemistry of genes, genetics and chromosomes.
Curiously it would not be Muller but another phage researcher, Salvador Luria, who would now give shape and direction to the young scientist’s growing infatuation with the gene.
The Italian-born Luria was another European scientist – a microbiologist, like Avery – who found refuge in America from the European war zone. By now he had entered into a working collaboration with Max Delbrück, who was Professor of Biology at the California Institute of Technology. In 1943 Luria and Delbrück designed and conducted an experiment that demonstrated that genetic inheritance in bacteria followed precise evolutionary principles. This experiment became one of the foundation stones of modern Darwinism. That same year Delbrück befriended another microbiologist called Alfred Hershey, who would subsequently write the key DNA paper with Martha Chase. In a letter to Luria, Delbrück summarised Hershey as follows: ‘Drinks whiskey but not tea. Likes living in a sailboat … Likes independence.’ The three scientists joined forces to become the nucleus of a cooperating and mutually supportive network of scientists that would become known as the ‘phage group’. Delbrück would subsequently explain that they would be a group only in the sense that they communicated freely on a regular basis, and that they told one another what they were thinking and doing. In this way a loose creative movement grew around the two European expatriate scientists, all working towards the common ambition of figuring out how genes worked.
Luria, Delbrück and Hershey now posed some interesting questions. How does the phage virus actually get into the bacterium? How, once inside, does it multiply? Does it multiply like a bacterium, growing and budding off daughter viruses? Or does it multiply by an entirely different mechanism? Is this multiplication some complex physical or chemical process that could be understood in terms of known physical and chemical principles? Through making use of the phage reproductive system, they hoped to solve the mystery of the gene. To begin with it all seemed simple in principle, but as experiment followed experiment and year followed year, they found themselves no closer to the answer.
Up to 1940 or so, people like Delbrück and Luria had assumed that viruses were simple. They had little to go on since the majority of viruses were so minuscule they could not be seen with any clarity through the ordinary light microscope. They would even talk about them as if they were akin to protein molecules. Luria would come to define phage viruses, in a misleading oversimplification, as extensions of the bacterial genome. But with the invention of the electron microscope, by the German company Siemens, even the smallest viruses, including bacteriophages, would soon become visible for the first time. And when they did become visible, they proved to be more complex than the two scientists had initially conceived.
Many phages had a head that was cylindrical in shape, with a narrow sheath below it, as tall as the head, and a base plate with six spikes with fibres attached. Now that they could visualise phages in the process of infecting their host bacteria, something struck Delbrück and Luria as exceedingly odd. The viruses didn’t actually pass through the bacterial cell wall. What they appeared to do was to squat down against the wall and inject their hereditary material into the cell. In 1951 a phage researcher called Roger Herriott would write to Hershey, ‘I’ve been thinking that the virus may behave like a little hypodermic needle full of transforming principles.’ This became the background to Hershey and Chase’s experiment in which they confirmed that that was precisely what happened. The virus behaved exactly like a hypodermic syringe; the tail and its elongated fibrils would attach to the bacterial wall and the phage would then inject its viral DNA in through the bacterial wall to take over the bacterium’s own genetic machinery, the viral genome compelling the bacterial genome to construct what was necessary for the generation of daughter viruses. In effect, the infected bacterium became a factory for the production of daughter viruses.
It would be this discovery, together with many associated extrapolations to microbiology and genetics, that would lead to all three scientists – Delbrück, Luria and Hershey – sharing the Nobel Prize in 1969.
Meanwhile, back in 1947, it was the dynamic energy and infectious charm of Luria, and the innovative genius of Delbrück, that proved most influential to the youthful Watson after his arrival into Indiana University. Still fascinated by the mystery of the gene, it was his hope that the mystery might be solved without his bothering to learn any of the complex physics or chemistry.
It is instructive to discover, from conversations between Luria and Watson, that there was no ignorance at Bloomington about Avery’s discovery of DNA. Luria had visited Avery in 1943, prior to the publication of the key paper, when he had the opportunity of discussing Avery’s findings in detail. He would recall Avery to Watson as an utterly non-pompous scientist, precise in his language, with a tendency as he spoke to close his eyes and rub his bald head – ‘every bit of a chemist, even though he was an MD’. Watson would take his cue from Luria, writing, in The Double Helix, how Avery had shown that hereditary traits could be transmitted from one bacterial cell to another by purified DNA molecules. Given the fact that DNA was known to occur in the chromosomes of every type of living cell, ‘Avery’s experiments strongly suggested that … all genes were composed of DNA.’
In the autumn of 1947, Watson, still just 19, took Luria’s course in bacteriology and Muller’s in X-ray-induced gene mutation. Faced with the choice of entering into research with Muller on Drosophila or with Luria on microbes, he plumped for Luria, despite the fact that the Italian scientist had a reputation among the graduate students for having a short fuse with dimwits. Watson would subsequently adopt his patron’s example. Delbrück was a heroic figure to Watson because he had inspired Schrödinger’s ideas in the inspirational book. Watson was delighted when Luria introduced him to Delbrück when the eminent German physicist paid a visit to Bloomington.
Luria set Watson a PhD dissertation on the pathological effects on phage of exposure to X-rays. The work proved so mundane that Watson would barely mention it in his biography. But his obsession with the gene was undimmed. By the summer of 1949, his thesis nearing completion, he had the itch to travel to Europe. Luria arranged a Merck Fellowship from the National Research Council – three thousand dollars for the first year, potentially renewable. In May the following year, with his PhD under his belt, he sailed for Denmark, where he had been assigned to study nucleotides with a biochemist named Herman Kalckar. Kalckar was a gifted scientist but his interest was neither the gene nor the bacteriophage. A disenchanted Watson switched his attentions to another Dane, and a member of the phage group, Ole Maaløe, who was working on the transfer of radioactively-tagged DNA from phages to their viral offspring.
Out of the blue, Kalckar accepted a short-term project in the Zoological Station in Naples. He suggested that Watson might tag along. Though he had little interest in marine biology, Watson was delighted to acquiesce. He hoped to warm himself in the Italian sun. But he was disappointed to find Naples chilly, with no heater in his room on the sixth floor of a nineteenth-century house. ‘Most of my time I spent walking the streets or reading journal articles … I daydreamed about discovering the secret of the gene, but not once did I have the faintest trace of a respectable idea.’
Here, by happenstance, he attended a lecture in the Zoological Station given by an English scientist named Maurice Wilkins. The lecture could hardly have excited him in prospect, knowing that most of it would be about the biochemistry of proteins. ‘Why should I get excited learning boring chemical facts as long as the chemists never provided anything incisive about the nucleic acids?’
But he took the risk and attended anyway.
Tall, bespectacled, asthenic and somewhat diffident in manner, you might have expected Wilkins’ presentation to bore the restless and impatient Watson. But it did not. To begin with, it was delivered in a language that Watson readily understood. And for all of his diffident manner, Wilkins kept to the point. Then suddenly, close to the end of the lecture, a projected slide jarred Watson to full attention. On the screen was a photograph that showed something Wilkins called an X-ray diffraction pattern of DNA that had been taken in the King’s College laboratory in London. Watson would subsequently admit that he knew nothing about X-ray crystallography. He hadn’t understood a word of what he had read about it in the scientific journals and he thought that much of what the ‘wild crystallographers’ were claiming was very likely baloney.
But now here was Wilkins mentioning in passing that this was the clearest picture of DNA that he and his colleagues had yet obtained from their X-ray studies. In the same audience was the Leeds-based English physicist, William Astbury, who had pioneered X-ray diffraction studies of biological molecules, and who had produced the first X-ray pictures of DNA. Astbury would subsequently confirm that no one had ever shown such a sharp, discrete set of reflections from the DNA molecule as Wilkins then projected onto the screen. ‘There was nothing like it in the literature.’ In explaining the picture, Wilkins suggested that DNA might be thought of as a crystalline substance.
Watson was electrified to hear Schrödinger’s prophecy confirmed. He sat in a daze of wonderment as Wilkins went on to explain that if and when we understood the structure of DNA, then we might be in a better position to understand how genes worked. Watson was now asking himself some pertinent questions. Who was this interesting English scientist, Wilkins? And how could he get to join his team at King’s College in London?
*
Maurice Hugh Frederick Wilkins was not, in fact, English, as Watson initially surmised. He was born in Pongaroa, New Zealand, where his father, Edgar Henry, was a practising doctor. The family were Anglo-Irish in origins, hailing from Dublin, where Maurice’s paternal grandfather had been headmaster of the high school and his maternal grandfather chief of police. On leaving New Zealand the family first returned to Ireland, then headed for London, where Dr Wilkins was later to do his pioneering work in public health.
Maurice had had a natural scientific curiosity even as a boy, and it was this curiosity that led to his studying physics as part of his BA at Cambridge University, after which he worked for his PhD under John Turton Randall (later knighted), a physicist who played a leading role in the development of radar during the war.
As a postgraduate, Wilkins moved to the University of Birmingham, following the posting of his Cambridge tutor, Randall, where the two scientists continued their collaboration on radar. But then, out of the blue, Wilkins found himself dispatched to the United States to work on the Manhattan Project. His purpose was to figure out how to purify suitable isotopes of uranium from impure sources, to make them suitable for the atomic bomb. In February 1944 Wilkins crossed the dangerous waters of the Atlantic on the Queen Elizabeth, heading for the University of Berkeley, California. Here he made a modest contribution to the development of the atomic bomb. However, the subsequent destruction of Hiroshima and Nagasaki by the very weapons that he had worked on left Wilkins somewhat unsettled in conscience.
After the war Wilkins returned to England, where he ended up as assistant director of the new Biophysics Unit at King’s College London, funded by the Medical Research Council, and where his former boss, Randall, was now the Wheatstone Professor of Physics. The new departmental remit was to apply the experimental methods of physics to important biological problems. This would result in Wilkins developing a relationship with Watson and Crick and joining the search for the molecular code of DNA. It would also involve him in a somewhat infamous strained working relationship with the X-ray crystallographer Rosalind Franklin.
Given this developing history, we might pause a moment or two to consider Wilkins’ personality, and its relevance to the com-ing storm. From what one can gather from his belatedly published biography, and the memory of those who knew him and worked with him, Wilkins was a quiet, highly moral man, somewhat Quaker-like in social attitudes. As a boy he enjoyed a close emotional relationship with his elder sister, Eithne, who taught him to dance. But this intimacy was torn apart when Eithne developed a bacterial infection that turned into a septicaemia, the blood-borne infection provoking septic arthritis in multiple joints. This would have been a shockingly painful and disabling condition, which, prior to antibiotics, might have proved fatal. She spent months in a hospital bed, with her limbs dangling from hoists, her joints lanced open to drain the pus. The unfortunate Eithne survived but the intimacy with her younger brother ended. The trauma of this experience may well have affected his self-confidence, particularly in his relationships with women.
While an undergraduate at Cambridge, he fell in love with a woman called Margaret Ramsey, but he ‘was incapable of making a suitable advance to her’. After he told her of his love, there was a short silence after which she walked from the room. During his stay in Berkeley, Wilkins was attracted to an artist named Ruth, who had shared lodgings with him. She conceived a child and they subsequently married, but when, as the war was ending, he informed Ruth that he intended to return to the UK, she refused to accompany him. ‘Ruth told me one day that she had made an appointment for me with a lawyer and when I arrived at his office I was shocked to hear that Ruth wanted to end our marriage.’ Shortly after the divorce, Ruth gave birth to a son. Wilkins went to see her, and their baby, in the hospital ward, before returning to the UK alone.
Wilkins would admit to difficulty overcoming an innate shyness, and he would require periodic psychotherapy in his time working at King’s, but he subsequently found a wife, Patricia, who appreciated the sensitive soul behind the diffident exterior, and he enjoyed a happy marriage and the joys of rearing a family of four children. There was also a fruitful outcome of his unsettled conscience following his work on the Manhattan Project. Before leaving Berkeley, one of his working colleagues came to his rescue … ‘Seeing I wanted to find some new direction, he lent me a new book with the rather ambitious title, What Is Life?’
four (#ulink_2a07bc6a-42b5-5437-9335-fbe67e5a89a5)
A Couple of Misfits (#ulink_2a07bc6a-42b5-5437-9335-fbe67e5a89a5)
Francis likes to talk … He doesn’t stop unless he gets tired or he thinks the idea’s no good. And since we hoped to solve the structure by talking our way through it, Francis was the ideal person to do it.
JAMES WATSON
It is somewhat ironic that Maurice Wilkins only arrived in Naples by happenstance, since he was substituting for Randall, who had agreed to present the talk but had been unable to attend. It seems unlikely, had Randall himself presented the lecture, that he would have included the DNA slide, or that he would have spoken of what it portrayed with such clear reference to Schrödinger’s book. This lecture, which so excited Watson, was on the physico-chemical structure of big biological molecules, mostly proteins, made up of thousands of atoms. The key photograph had been taken by Wilkins, working together with a graduate student called Raymond Gosling while using a technique called X-ray diffraction.
One of the things this technique was particularly good at was finding the sort of repetitive molecular themes you found in crystals, hence the other term for it: X-ray crystallography.
‘Suddenly,’ as Watson would later recall, ‘I was excited about chemistry.’
Up to this moment Watson had had no idea that genes could crystallise. To crystallise, substances must have a regular atomic structure – a lattice-like structure of atoms at the ultramicroscopic level. The youthful Watson appears to have been a wonderfully free spirit journeying from one interesting encounter to another. Impulsive, impatient, egregiously direct, yet all the while on the hunt for new adventure.
‘Immediately I began to wonder whether it would be possible for me to join Wilkins in working on DNA.’ But Watson never got to work with Wilkins. Instead, happenstance headed him in the direction of another X-ray crystallographer called Max Perutz, who was working at the Cavendish Laboratory at Cambridge University.
The Cavendish Laboratory is a world-famous department of physics. First established in the late nineteenth century to celebrate the work of British chemist and physicist Henry Cavendish, one of its founders and the first Cavendish Professor of Physics was James Clerk Maxwell, famous for his development of electromagnetic theory. The fifth Cavendish Professor and the director of the laboratory at the time of Watson’s arrival was William Lawrence Bragg, who was the successor, as director, to Lord Ernest Rutherford, another Nobel Prize-winner and the first physicist to split the atom. Bragg was an Australian-born physicist who, jointly with his father, had been awarded the Nobel Prize in Physics in 1915 for establishing the use of X-rays in analysing the physico-chemical structures of crystals. X-ray beams are bent when they pass through the orderly atomic lattice of crystals. What is projected onto the photographic plate is not the picture of the atoms within the structure but the refracted pathways of the X-rays after they have collided with the atoms. This is called ‘diffraction’ and is similar to how light is bent when it passes through water. In a structure with haphazard positioning of atoms in space, the X-rays will be scattered randomly and form no pattern. But in a structure that contains atoms in a repetitive atomic lattice – such as a crystal – the X-rays are deflected in a recognisable pattern of blobs on the X-ray plate. From this diffraction pattern, the atomic structure of the structure can be deduced.
The two Braggs – father and son working as a team at the University of Leeds – had constructed the first X-ray spectrometer, allowing scientists to study the atomic structure of crystals. At the age of 22, Bragg Junior, now a Fellow of Trinity at Cambridge, had produced a mathematical system, Bragg’s Law, that enabled physicists to calculate the positions of the atoms within a crystal from the X-ray diffraction pictures. At the time of Watson’s arrival into the laboratory, Bragg’s main focus of study was the structure of proteins. It was this potential for the X-ray diffraction of proteins that had attracted Max Perutz to the Cavendish Laboratory.
Born in Vienna of Jewish parentage, Perutz was another enforced exile who had settled in England and become a research student at the Cavendish Laboratory. He completed his PhD under Bragg and subsequently devoted most of his professional life to the analysis of the macromolecule of haemoglobin, the pigment that colours the red cells in our blood, enabling them to carry oxygen around the body. Also working at the Cavendish was an unusual young scientist, Francis Crick. The English-born scientist had graduated with a BSc in physics from University College London aged 21, but thanks to war duty and a profound antipathy to his PhD project (he was supposed to be working on the viscosity of water at high temperatures) he, like Watson, found an alternative source of inspiration in Schrödinger’s book. In Crick’s own words, ‘It suggested that biological problems could be thought about in physical terms.’
But what terms?
At the time Crick wasn’t as convinced by Avery’s discovery as Watson was. Like Schrödinger himself, Crick was more inclined to the protein hypothesis. But he was every bit as impressed with Schrödinger’s ‘code-script’ idea as Watson. What then could he possibly make of Schrödinger’s conception of an aperiodic crystal?
Simple crystals such as sodium chloride, the basis of common salt, would be incapable of storing the vast memory needed for genetic information because their ions are arranged in a repetitive or ‘periodic’ pattern. What Schrödinger was proposing was that the ‘blueprint’ of life would be found in a compound whose structure had something of the regularity of a crystal, but must also embody a long irregular sequence, a chemical structure that was capable of storing information in the form of a genetic code. Proteins had been the obvious candidate for the aperiodic crystal, with the varying amino acid sequence providing the code. But now that Avery’s iconoclastic discovery had been confirmed by Hershey and Chase, the spotlight fell on DNA as the molecular basis of the gene. Suddenly new vistas of understanding the very basics of biology, and medicine, appeared to be beckoning.
It was through a mixture of luck and the gut reaction of Perutz that the dilettantish Crick was taken into the fold of the Cavendish. In Perutz’s recollection, Crick arrived in 1949 with no reputation whatsoever in science. ‘He just came and we talked together and John Kendrew and I liked him.’ And so the likeable Crick ended up, in such an idiosyncratic process of selection, working on the physical aspects of biology – what today we call molecular biology – under the guidance of Bragg, Perutz and Kendrew, at the Cambridge laboratory.
In 1934, John Desmond Bernal, an Irish-born scientist with Jewish ancestry and a student of Bragg Senior, had shown for the first time that even complex organic chemical molecules, such as proteins, could be studied using X-ray diffraction methods. Bernal was a Cambridge graduate in mathematics and science, who was appointed as lecturer to Bragg at the Cavendish in 1927, becoming assistant director in 1934. Together with Dorothy Hodgkin, Bernal pioneered the use of X-ray crystallography in the study of organic chemicals – the chemicals involved in biological structures – including liquid water, vitamin B1, the tobacco mosaic virus and the digestive enzyme, pepsin. This was the first protein to be examined at the Cavendish in this way. When, in 1936, Max Perutz arrived as a student from Vienna, he extended Bernal’s work to the X-ray study of haemoglobin.
By the time Crick joined the laboratory, Sir William Bragg had been replaced by Sir Lawrence Bragg, and John Kendrew and Max Perutz had taken Bernal’s findings further to become bogged down in a ‘disastrous paper’ on the chain structures of proteins. And now we discover something distinctly unusual about Francis Crick, something that Perutz may have intuited at their meeting. He had an avid curiosity about science, reading very widely, and he was equipped with a mind capable of amassing a formidable knowledge base across different disciplines. One of the first things he did after his arrival into the Cavendish was to acquaint himself with everything his bosses had achieved. Junior as he was, Crick now took it upon himself to undertake a long, critical look at their work. This he then proceeded to criticise from basic principles. At the end of his first year in the department, Crick presented his criticisms in the form of an ad hoc seminar, borrowing his title from Keats as ‘What Mad Pursuit’. He began with a twenty-minute summary of the deficiencies in the departmental methods before pointing out what he saw as the ‘hopeless inadequacy’ of their investigation of the structure of the haemoglobin molecule. The X-ray analysis of haemoglobin was of course Perutz’s main objective. Bragg was infuriated by the cocky behaviour of this upstart junior colleague, but Perutz would subsequently admit that Crick was right and proteins were far more complicated in their structures than they had initially assumed. Restless and ever-inquisitive, Crick proved to be an uneasy, sometimes downright embarrassing import into the scientific pool of the laboratory. And while Bragg and Perutz saw proteins as the great unsolved puzzle, Crick was more interested in the mystery of the gene.
As 1949 elided into 1950, Crick would subsequently confess that he still did not realise that the genetic material was DNA. But he knew that genes had been plotted out in linear arrays along the chromosomes by people like Barbara McClintock, and that proteins, which had to be the expression of the genes, were also being plotted out as linear arrays, however lengthy and complicated. There had to be some logical way in which one translated into the other. By 1951, two years after his arrival into the Cavendish Laboratory, Crick perceived that these were two different, if necessarily related, puzzles – the mystery of how genes appeared able to copy themselves, and the mystery of how the linear structures of genes translated into the linear structures of proteins.
The wide-reading, voraciously inquisitive Crick needed what Judson termed a catalyst. This arrived in the form of the gangly, equally inquisitive Watson that same year, 1951. From their first meeting, it would appear that here was one of those rare working conjunctions of two odd-ball personalities that, when they come together, make an extraordinary creative whole that is more than the sum of the individual ingenuities. And yet it very nearly didn’t happen.
*
We should recall that Watson was extremely junior within the department. A recent PhD graduate, he had arrived into Kalckar’s laboratory on a Merck Fellowship funded by the US National Research Council. The terms and conditions were laid down and signed for back home, but now here he was abandoning those carefully laid intentions to gallivant from the work in Denmark to follow some giddy new inspiration in England, a place he had never visited in his life and where he knew absolutely nobody. Impulsive and single-minded, Watson would subsequently confess that his head was filled with curiosity about that single DNA photograph. He had tried to engage with Wilkins in Naples after the lecture, at a bus stop during an excursion to the Greek temples at Paestum. He had even tried to take advantage of a visit from his sister, Elizabeth, who had arrived to join him as a tourist from the States. Now here were Maurice Wilkins and Watson’s sister, Elizabeth, finding a common table to take lunch together. Watson sensed an opportunity and barged in, with the intention of ingratiating himself with Wilkins. But the self-effacing Wilkins excused himself, to allow brother and sister the privacy of the table.
His plans foiled, Watson refused to let go of this exciting new avenue of interest. ‘I proceeded to forget Maurice, but not his DNA photograph.’
He stopped over in Geneva for a few days to talk to a Swiss phage researcher, Jean Weigle, who provoked yet more excitement by informing Watson that the eminent American chemist, Linus Pauling, had partly solved the mystery of protein structure. Weigle had attended a lecture by Pauling, who like Bragg in Cambridge had been working with X-ray analysis of protein molecules. Pauling had just made the announcement that the protein model followed a uniquely beautiful three-dimensional form – he had called it an ‘alpha-helix’. By the time Watson arrived back in Copenhagen, Pauling had published his discovery in a scientific paper. Watson read it. Then he re-read it. He was confounded by his lack of understanding of X-ray crystallography. The terminology, in physics and chemistry, was so far beyond him that he could only grasp the most general impression of its content. His reaction was so childishly naïve as to be touching: in his head he devised the opening lines of his own imagined paper in which he would write about his discovery of DNA, if and whenever he discovered something of similar portent.
But what to do to get on board the DNA gravy train?
He needed to learn more about X-ray diffraction studies. Ruling out Caltech, where Pauling would react with disdain to some ‘mathematically deficient biologist’, and now ruling out London, where Wilkins would be equally uninterested, Watson wondered about Cambridge University, where he knew that somebody called Max Perutz was following the same X-ray lines of investigation of the blood protein molecule, haemoglobin.
‘I thus wrote to Luria about my newly found passion …’
The world of science was smaller in 1951 than it is today. Even so, it would appear a hopelessly optimistic ambition for this impulsive young graduate to merely ask his mentor to fix his arrival into a leading laboratory in England to engage in a line of research that he knew absolutely nothing about.
The amazing outcome was that Luria was able to do so. By happenstance, he met Perutz’s co-worker, John Kendrew, at a small meeting at Ann Arbor, in Michigan, where, by a second and equal happenstance, there was a meeting of minds – both scientific and social. And by a third happenstance, Kendrew was looking for a junior to help him study the structure of the muscle-based protein myoglobin, which contained iron at its core and held on to oxygen, just like the haemoglobin in the blood.
Twice in his short career the young American scientist had leapt into the unknown and landed on his feet. First it had been through Luria’s patronage in Bloomington, and by extension also Delbrück’s, two of the co-founders of the phage group; and now the gift of happenstance extended further, again through Luria’s patronage, to Kendrew, and by proxy to the Cambridge laboratory and Max Perutz. Watson’s arrival into the laboratory would bring him under the ultimate tutelage of Sir Lawrence Bragg, a founder of X-ray crystallography. It would connect him directly to his future partner in DNA research, Francis Crick, and further afield – through the connection between the Cambridge laboratory and the X-ray laboratory at King’s College London – with Maurice Wilkins and a young female scientist, Rosalind Franklin, who were working on the X-ray crystallography of DNA.
five (#ulink_191c9ae8-887d-5869-af27-b063095aa353)
The Secret of Life (#ulink_191c9ae8-887d-5869-af27-b063095aa353)
I think there was a general impression in the scientific community at that time that [Crick and Watson] were like butterflies flicking around with lots of brilliance but not much solidity. Obviously, in retrospect, this was a ghastly misjudgement.
MAURICE WILKINS
In the opening pages of his brief, witty and brutally candid autobiography, James Watson recounts a chance meeting in 1955 with a scientific colleague, Willy Seeds, at the bottom of a Swiss glacier. It was two years after the publication of the discovery of DNA. Watson and Seeds were acquainted, Seeds having worked with Maurice Wilkins in probing the optical properties of DNA fibres. Where Watson had anticipated the courtesy of a chat, Seeds merely remarked, ‘How’s Honest Jim?’, before striding away. The sarcasm must have bitten deep for Watson to not merely remember it distinctly, but even to consider the term ‘Honest Jim’ as the initial title of his life story, before being persuaded to adopt the more descriptive alternative, ‘The Double Helix’. It was as if the former colleague was questioning Watson’s right to be recognised as the co-discoverer of the secret of life.
He had been taken aback, reflecting on meetings with the same colleague in London a few years earlier, at a time when, in Watson’s words, ‘DNA was still a mystery, up for grabs … As one of the winners, I knew the tale was not simple, and certainly not as the newspapers reported.’ It was a more curious story, one in which his fellow-discoverer, Francis Crick, would freely admit that neither he nor Watson was even supposed to working on DNA at the time. Equally curious was the fact that up to the day of the discovery, neither Watson nor Crick had contributed anything much to the many different scientific threads and themes that, when finally put together, like the pieces of a remarkable three-dimensional jigsaw puzzle, laid the molecular nature of DNA bare for the first time in history.
Watson’s welcome into the Cambridge laboratory was quintessentially English in its lack of formality. He arrived in Perutz’s office straight from the railway station. Perutz put him at his ease about his prevailing ignorance of X-ray diffraction. Both Perutz and Kendrew had come to the science from graduation in chemistry. All Watson needed to do was to read a text or two to become acquainted with the basics. The following day Watson was introduced to the white-moustached Sir Lawrence, to be given formal permission to work under his direction. Watson then returned to Copenhagen to collect his few clothes and tell Herman Kalckar about his good luck. He also wrote to the Fellowship Office in Washington, informing them of his change of plans. Ten days after he had returned to Cambridge he received a bombshell in the post: he was instructed, by a new director, to forgo his plans. The Fellowship had decided he was unqualified to do crystallography work. He should transfer to a laboratory working on physiology of the cell in Stockholm. Watson appealed once more to Luria.
As far as Watson was concerned it was out of the question to follow these new instructions. If the worst came to the worst, he would survive for at least a year on the $1,000 still left to him from the previous year’s stipend. Kendrew helped him out when his landlady chucked him out of his digs. It was just another indignity when he ended up occupying a tiny room at Kendrew’s home, which was unbelievably damp and heated only by an aged electric heater. Though it looked like an open invitation to tuberculosis, living with friends was preferable to the sort of digs he might be able to afford in his impecunious state. And there was a comfort to be had:
‘I had discovered the fun of talking to Francis Crick.’
And talk they did.
In Crick’s own memory: ‘Jim and I hit it off immediately, partly because our interests were astonishingly similar and partly, I suspect, because a certain youthful arrogance, a ruthlessness, and an impatience with sloppy thinking came naturally to us both.’ That conversation, lasting for two or three hours just about every day for two years, would unravel the most important mystery ever in the history of biology – the molecular basis of heredity.
We need to grasp a few fundamentals to understand how this happened. Firstly, we have two young and ambitious men – in Watson’s case aged just 23, in Crick’s, aged 35 – who were both exceptionally intelligent and surrounded by the ambience of high scientific endeavour and achievement. We need to grasp that Watson’s interest, intense and obsessive, was the structure of DNA in its potential to explain the mystery of the workings of the gene, and thus the storing of heredity. We also need to grasp the slight, but important, difference with Crick’s interest, which was not DNA, or even the gene in itself, but the potential of DNA to explain how Schrödinger’s mysterious molecular codes – his aperiodic crystals – had the potential not only for coding heredity but for translating from one code to another, from the gene to the second aperiodic crystal that must determine the structure of proteins.
Crick would subsequently recall Watson’s arrival in early October 1951. Odile, his French second wife, and he were living in a tiny ramshackle apartment with a green door that they had inherited from the Perutzes. Conveniently situated for the centre of Cambridge and only a few minutes’ walk from the Cavendish Laboratory, it was all they could afford on Crick’s research stipend. The ‘Green Door’, as it was thereafter called, consisted of an attic over a tobacconist’s house, with ‘two and a half rooms’ and a small kitchen that was reached by climbing a steep staircase off the back of the tobacconist’s house. The two rooms served as living room and bedroom for Crick and Odile, with the half room providing a bedroom for Crick’s son, Michael – born to his first wife, Ruth Doreen – when Michael was home from boarding school. The wash-room and lavatory opened halfway up the stairs and the bath, covered with a hinged board, was a feature of the tiny kitchen.
One day, out of the blue, Perutz brought Watson to the flat. Crick was out. But he would recall Odile remarking that Max had come round with a young American who ‘had no hair’. The newly arrived Watson was sporting a crew-cut – a hairstyle uncommon in England at the time. They met within a day or two … ‘I remember the chats we had over those first two or three days in a broad sort of way.’
Both men were impecunious, but it hardly mattered since they were uninterested in money. What mattered was that the deeply personal, deeply intellectual, symbiosis had begun. Crick brought a rowdy enjoyment of problem solving, together with the hubris, born out of his background in physics, to believe that the big problem facing them – the mystery of the gene – was indeed solvable. Watson, who had little knowledge of physics or X-ray crystallography, brought a mine of knowledge about the way in which genes worked – the fruits of the bacteriophage researches of Luria and Delbrück. Perutz would subsequently confirm that the arrival of Watson, at that particular moment of time, was opportune for the workings of the Cavendish Lab, where his enthusiastic personality appeared to have galvanised Crick, and where his knowledge of the field of genetics added an exotic aspect to the structural physics and chemistry that otherwise prevailed. Moreover, different as their backgrounds were, Crick and Watson shared a deep, insatiable level of curiosity about the puzzle that lay at the very root of biology: they were determined, almost from their first meeting, that they would solve the mysterious nature of the gene.
The first creative step was to realise that the answer lay with DNA. To be more accurate, they realised that somehow chemical structure must parallel function: so the answer to the great conundrum lay in the three-dimensional chemical structure of DNA. But nobody really knew what shape or form this structure took. To the minds of Crick and Watson at that particular moment in time, it would have seemed nothing more than a ghost in the mist.
New discoveries in science will usually involve a lengthy period of laboratory labour, with knowledge growing by hard-won increments, often involving contributions from several, or a good deal more than several, different sources. In many ways the struggle to get to grips with the mysteries of heredity followed exactly such a course. But the mundane sweat of the laboratory aspects, the growth of knowledge by hard-won increments, would not fall to Watson and Crick. These would be left to others. The Crick–Watson symbiosis would be founded on a second, equally important ingredient of scientific advance, and one that has commonalities with the advances in the arts and humanities: this is the quintessentially human gift we call ‘creativity’.
Within the hierarchy of the lab, Crick and Watson were the lowest contributing level. In Crick’s words, ‘I was just a research student and Jim was just a visitor.’ They read very widely, imbibing the fruits of the hard work of others. They talked and talked, thinking out loud, probing one another’s ideas and knowledge, often with Crick playing devil’s advocate. In fact they gossiped and argued so much they were given a room to themselves – to avoid their interrupting the thoughts of their more senior colleagues – within the crowded structure of the old Cavendish Laboratory. The X-ray laboratory, with its heavy machinery and radiation dangers, was located in the basement. Jim and Francis would also share a cheap and cheerful lunch, of shepherd’s pie or sausage and beans, at the local pub, the Eagle – a grubby establishment in a cobblestoned courtyard – where the creative debate would simply continue.
What little they knew about DNA was made even more uncertain by the fact that Crick believed that much of what was generally assumed to be the case with DNA and heredity was almost certainly wrong. It had been this attitude that had got him into trouble with Bragg. It meant that he didn’t even trust the work of his seniors here in the lab. But the real reason behind Bragg’s anger was his resentment of the fact that the chemist, Pauling, had discovered the alpha helix of protein. Meanwhile, Crick was convinced that the reason why the Cavendish had missed out on this was because they were assuming the accuracy of some earlier experimentation on the X-ray interpretation of the skin protein, keratin, which is the main ingredient of our human nails and a raptor’s claws. The way in which Crick’s mind worked can be gleaned from a remembered conversation:
‘The point is [so-called] evidence can be unreliable, and therefore you should use as little of it as you can. We have three or four bits of data, we don’t know which one is reliable … [What if] we discard that one … then we can look at the rest and see if we can make sense of that.’
*
Watson joined the Cavendish in the same year, 1951, in which Linus Pauling published his paper on the protein ‘alpha helix’. This discovery so rattled Watson that all of the time he was working with Crick on the structure of DNA, he was looking over his shoulder in Pauling’s direction.
He had good reason for seeing Pauling as the supreme rival in such an exploration; awarded the Nobel Prize in Chemistry in 1954, Pauling was already being hailed by scientific historians as one of the most influential chemists in history. His master work, though he contributed a great deal more, was to apply a quantum theory perspective to the chemical bonds that bind atoms within the structure of molecules, extending this basic science to the complex organic molecules that are the chemical building blocks of life.
The twentieth century has amazed us with its achievements in astronomy, in which scientists have plotted the stars and galaxies, and the forces, such as black holes, that govern the Universe. Equally important, though not so easily recognised as such by the ordinary man and woman, have been the achievements of the chemists and biochemists in exploring the micro-universe of atoms and molecules. Two forces in particular play a key role in the way that atoms bind to one another to make up life’s particular molecules. One of these is called the covalent bond; the other is called the hydrogen bond. Pauling applied the science of quantum mechanics to the forces involved in these two very different chemical bonds.
We have no need to concern ourselves with the complex mathematics of the applied physics. We just need to grasp the basic mechanics. And where better to look than at the familiar molecule of water.
Everybody knows that the chemical formula for water is H
O. This tells us that a molecule of water comprises one atom of oxygen and two atoms of hydrogen. But how do they link with one another to form the stable compound that we handle and consume every day of our lives? The molecule of water might be compared to a planet, oxygen, with two encircling moons of hydrogen. In such a situation, we can readily imagine how the force of gravity would hold the hydrogen moons to their orbits around the oxygen planet. In molecular terms, the forces holding the two hydrogen atoms to the oxygen atom are called ‘covalent bonds’. At the ultramicroscopic level of atoms, the nucleus of each hydrogen atom contains a single positively charged proton while circling around the nucleus is a single negatively charged electron. Meanwhile, the oxygen atom has eight positively charged protons within its nucleus and eight balancing, negatively charged electrons in orbits around it. These electrons occupy two orbits – two electrons taking up an inner orbit and six taking up an outer orbit. In coming together to form a molecule of water, the two electrons in orbit around each of the two hydrogen nuclei have paired with two of the six electrons of the oxygen outer orbits. The paired electrons share their attraction to the protons of the two parent nuclei, so the paired electrons are now equally attracted to the oxygen nucleus and the hydrogen nuclei. This sharing of attraction creates a stable ‘covalent’ bond between the three atoms, just as gravity created stable orbits for the two moons rotating around our imaginary planet of oxygen.
Hydrogen bonds are something else.
Once again, we might take water as our example. But here we are looking at the chemical interactions between whole water molecules – the H
Os reacting with one another. There are forces of attraction, albeit rather weaker and less stable than covalent bonds, between certain molecules that contain both hydrogen and heavier atoms such as nitrogen, oxygen or fluorine. Since water contains hydrogen and oxygen, these hydrogen bonds can form between molecules of water – it is this sticking together of water molecules that explains the difference between water vapour, or steam, liquid water and solid water, or ice. In ice most of the molecules are attached to one another by hydrogen bonds, to form something like a crystal; in liquid water varying amounts are attached to one another; and in steam, as a result of the addition of energy through heating, the hydrogen bonds linking water molecule to water molecule are broken down but the covalent bonds linking atoms to atoms remain intact.
We see that hydrogen bonds are weak, and thus unstable when heated, but covalent bonds are stable. These same two bonds, covalent and hydrogen bonds, are important ingredients in the structure of organic chemicals such as proteins. And they are also important in the structure of DNA.
Between 1927 and 1932, Pauling published some fifty scientific papers in which he conducted X-ray diffraction studies, coupled with quantum mechanical theoretical calculations, leading him to postulate five rules, known as Pauling’s rules, that would help science to predict the nature of the bonds that held together atoms within molecules. At least three of these rules were based on Bragg’s own work, the purloining of which provoked Bragg to fury. It was now inevitable that there would be ongoing scientific rivalry between the two scientists. Pauling’s work into the nature of chemical bonding was so original, and pioneering, that he was awarded the Nobel Prize in Chemistry in 1954. Meanwhile, this new level of understanding enabled Pauling to visualise the precise shape and dimensions of molecules in three-dimensional space. Working at Caltech, Pauling applied this to the huge molecules of proteins, using the techniques of X-ray diffraction analysis pioneered by the Braggs. He showed, for example, that the haemoglobin molecule – the focus of Perutz’s research – changed its physical structure when it gained or lost an oxygen atom. And Pauling continued to apply his rules to researching the molecular structure of proteins.
Pioneering X-ray pictures of fibrous proteins had been obtained some years before at the University of Leeds by William Thomas Astbury, the physicist who had attended Wilkins’ talk in Naples, but it was assumptions based on these X-ray diffraction pictures that Crick was now questioning at the Cavendish Laboratory. For many years Pauling had tried to apply quantum mechanics calculations to Astbury’s X-ray pictures, but he found that things just didn’t add up. It would take him and two collaborators, Robert Corey and Herman Branson, fourteen years before they made the necessary breakthrough.
All proteins have a primary structure that is made up of an amino acid code, with the letters made up of twenty different amino acids. The chemical bonds that join up the amino acids into the primary chain are called ‘peptide bonds’. Pauling and his collaborators now realised that peptides bonded together in a flat two-dimensional plane – they called this ‘a planar bond’. A problem with outdated equipment had caused Astbury to make a critical error in taking his X-ray pictures: the protein molecules became tilted away from their natural planes, skewing the mathematical extrapolations of their structure. Once they had corrected Astbury’s error, Pauling and co discovered that as the chain of amino acids grew, to form the primary structure of proteins, it naturally followed the shape of a coiled spring, twisting to the right – the so-called ‘alpha helix’. This was the discovery that had excited Watson on his return trip from Naples.
Back in Cambridge, Sir Lawrence Bragg was bitterly disappointed when Pauling’s group beat his to the discovery of the primary structure of proteins. But there was a silver lining to the cloud: Perutz now used Pauling’s breakthrough to reappraise his own work on the haemoglobin molecule, a reappraisal that would solve the structural puzzle of haemoglobin and garner his Nobel Prize in Chemistry in 1963. Pauling’s discovery also alarmed Watson who, from his arrival at Cambridge, had assumed that they had a very knowledgeable and powerful rival in what was now a race to discover the three-dimensional structure of DNA.
*
But the problem, as Crick would point out in their day-to-day sharing of thoughts and incessant debate, was that they couldn’t even assume that Pauling’s data was right. In Crick’s words, ‘Data can be wrong. Data can be misleading.’ So Crick and Watson attempted to construct their physical model with a sceptical eye on prevailing experimental data. To put it another way, they relied just as heavily on creative leaps of their own imagination as on existing experimental data.
Crick and Watson were now asking themselves if DNA, like proteins, had a helical structure, and Watson in particular was convinced that they should also take their cue from Pauling, who liked to construct three-dimensional models of the molecules he was attempting to envisage. To do so they would have to think, as Pauling did, about the atomic structures that made up the chemistry of DNA – to fit the molecules, with their component atoms, and the bonds between them, into a complex three-dimensional jigsaw. They knew that they were dealing with the four nucleotides – guanine, adenine, cytosine and thymine – together with the molecule of the sugar, called ribose, and the inorganic chemical, phosphate, all of which, when correctly fitted together, must somehow make up the mysterious three-dimensional jigsaw puzzle.
Two relevant questions now loomed. Firstly, if the structure was helical, what kind of helix was involved? And secondly, where did the phosphate molecule fit into the structure? Calcium phosphate is the mineral of bones, of shells, of rocks formed from the remains of living marine organisms – limestone. The presence of phosphate suggested some kind of strengthening of the DNA chain – a chemical scaffold – maybe a spine? But where did this spine lie in relation to the presumptive and as yet unknown spiral? And where, or how, did the sugar fit in? The code itself must surely lie with the nucleotides, acting perhaps as something like letters. Each was a key ingredient, but how on earth did the whole thing assemble in a way that made sense?
An important clue must come from the X-ray diffraction patterns. That meant they needed the help of Maurice Wilkins and Rosalind Franklin – ‘Rosy’, as Watson referred to her in his autobiography – who were conducting X-ray analyses of DNA fibres at the King’s College London laboratory.
*
Rosalind Elsie Franklin was born in London to a prosperous Jewish family in 1920. From an early age she showed both a brilliantly incisive mind and the stubbornness necessary to make a distinguished mark for herself. She also showed an aggressively combative side to her personality that might prove a mixed blessing in overcoming the prevailing prejudices against Jews in society, as well as against women being in higher education and the scientific workplace. It didn’t help that her father, who appeared to be a similarly combative character to his daughter, opposed her notion of a career in science. In her second year at Newnham College, Cambridge, he threatened to cut off her fees, urging that she switch to some practical application in support of the war effort. Only when he was dissuaded by her mother and aunt did he relent and allow her to continue her course.
Franklin studied physical chemistry, which involved lectures, extensive reading and laboratory experience in physics, chemistry and the mathematics that applied to these disciplines. One of the mandatory texts she read was Linus Pauling’s The Nature of the Chemical Bond.
The youthful Rosalind Franklin was disappointed when she ended up with a good second, and not a first, ‘bachelor’s’ degree in 1941. Even then, such was the lingering prejudice against female graduates in science that she was forced to wait in an unseemly uncertainty, one shared with all previous female graduates of Newnham, until her due qualification was formally granted, retrospectively, in 1947.
Like Francis Crick, Franklin was seconded to National Service during the Second World War, studying the density and porosity of coal for a PhD, in which she helped to classify different types of coal in terms of fuel efficiency. Post-war, she followed this up with a research stint working under the direction of Jacques Mering at the Laboratoire Central des Services Chimique de l’Etat, in Paris. Here, Mering introduced her to the world of X-ray crystallography which he used to study the structure of fibres, such as rayon. ‘With his high tartar cheekbones, green eyes and hair combed rakishly over his bald spot’, Franklin was surprised to discover that Mering was Jewish, as well as being ‘the archetypal seductive Frenchman’. The still youthful, and perhaps naïve, Rosalind Franklin appears to have fallen in love with Mering, who was already married, but whose wife was ‘nowhere in evidence’.
Brenda Maddox, one of Franklin’s biographers, would draw attention to the fact that Franklin’s most imaginative and productive research was conducted when she was teamed up with male scientists of Jewish background. Mering also appeared to be attracted to the trim, slender young woman, with the lustrous dark hair and glowing eyes. They would spend entire days and on into the evenings deep in discussion and argument over likely meanings of X-ray plates and atomic structures.
However, Franklin’s infatuation with Mering would be painfully halted when, in January 1951, she took up a post as research associate at King’s College London in the Medical Research Council Biophysics Unit, directed by John Turton Randall. Her appointment happened to coincide with a major post-war rebuilding within the department, designed to accommodate new ambitions within the nascent field of biophysics. The precise nature and purpose of her appointment has since become the subject of debate. In part some confusion has arisen because Randall changed the scope of her appointment in between first confirming it and Franklin taking up the post. She had initially agreed to carry out X-ray diffraction studies of proteins, but Randall wrote to her before she took up her appointment, suggesting that she change direction to the study of DNA. According to Maurice Wilkins, this was at his suggestion. Whether at Wilkins’ suggestion or Randall’s own idea, Franklin agreed. She was offered the assistance of a promising graduate student, Raymond Gosling, to work with. But there was an inherent problem with this new direction.
Wilkins, who was Deputy Director of the MRC Unit based at King’s College, was the same scientist who had first lit the fuse of inspiration for Watson in the 1950 Naples lecture. Wilkins had initiated the research into DNA in the department, but happened to be deputising once again for Randall in America at the time of Franklin’s appointment. Up to now Gosling had been working with Wilkins on DNA; even after his return from America, Randall failed to inform Wilkins about the terms he now proposed for Franklin’s job description. This led to what Franklin’s later research colleague, Aaron Klug, would describe as ‘an unfortunate ambiguity about the respective positions of Wilkins and Franklin, which later led to dissension between them and about the demarcation of the DNA research at King’s’.
This is a short quote from the typed letter from Randall to Franklin, specifying her working conditions:
… as far as the experimental X-ray effort is concerned there will be at the moment only yourself and Gosling, together with the temporary assistance of a graduate from Syracuse, Mrs. Heller …
While this clearly suggests that Franklin was expected to take on the X-ray diffraction work, the qualification ‘at the moment’ is too vague to interpret. But there is nothing in this letter to suggest that Franklin should ignore the work performed by Wilkins, or that she should refuse to collaborate with the rest of the department in her approach to the DNA problem.
Wilkins, working with Gosling, had initiated the X-ray diffraction studies on DNA in the department, and in particular obtaining the best resolution diffraction photographs that existed up to this date. They had demonstrated a key property of DNA – that it had a regular, crystal-like molecular structure. In Paris Franklin had learned, and improved upon, X-ray diffraction techniques for dealing with substances of limited order. But even Klug, an ardent supporter of Franklin, admitted that in relation to the work conducted by Franklin in Paris, ‘It is important to realise … Franklin gained no experience of such formal X-ray crystallography.’
Back in early 1950 Wilkins had complained of poor-quality X-ray apparatus that was not designed for the scrutiny of exquisitely fine fibres. At his suggestion, the department had purchased a new and better-quality X-ray tube to be set up in the basement, but it had lain there for a year or more unused while Wilkins was distracted by the multiple tasks that fell to a busy deputy director of the unit. On her arrival, Franklin, not unnaturally, believed that she was there to take over the DNA work as her personal project. However, the returning Wilkins expected that Franklin had been brought in as his collaborator, to take up the research from where he had already developed it. He would subsequently admit that he was unqualified to take the X-ray diffraction work further and needed exactly such a dedicated and qualified collaborator. ‘That’s why we hired Rosalind Franklin.’
Unfortunately, Franklin and Wilkins now disagreed as to her role. Even so, rancour was neither necessary nor inevitable between the two scientists, personally or scientifically. These difficulties, provoked by Randall’s vagueness, might have been readily overcome with goodwill on both sides, but Franklin, in the opinion of both her biographers, was not inclined to cooperate.
Much has been written about prejudicial attitudes to women in science at this time. In particular an American journalist, and personal friend of Franklin’s, Anne Sayre, would write a biography of her in which she suggested that King’s College was particularly unfriendly to female scientists, with Franklin struggling to assert her presence in a domain that was almost exclusively male. But when another American journalist, Horace Freeland Judson, looked into this claim, he discovered that of the 31 staff working at King’s at this time, eight were female, including some working in a senior position in Franklin’s unit. A second biography of Franklin, by Brenda Maddox, confirmed that women were, on the whole, well treated at King’s College. Crick made the same point in his biography – and Crick had come to know Franklin well in the years following the DNA discovery. Even in Sayle’s more trivial complaint – that the main dining room was exclusively forbidden to women, who were thus precluded from lunchtime conversation – is misleading. There were two dining rooms. One was limited to men, but this, in the main, was used by Anglican trainees. The main dining room, used by the departmental staff, including Randall himself, was open to all.
The frosty relationship between Wilkins and Franklin was not the result of anti-female prejudice – it even seems unlikely to be the result of Randall’s peculiar wording in the letter – but it appears to be more directly related to a personality clash between the two scientists. Of the two, only Wilkins ever seems to have made any attempt at compromising. He asked other colleagues what he should do, but Alexander (Alec) Stokes, his closest colleague, was even meeker than he was. In Brenda Maddox’s opinion, the two should have got on well; Wilkins was gentle in manner and, despite his lack of self-confidence, was attractive to women. He was mathematically fluent and immersed in the very problems that concerned Franklin. But ‘confrontation’, in Maddox’s words, ‘was Franklin’s tactic, whenever cornered’. In an earlier confrontation with her professor, R. G. W. Norrish, when working on a postgraduate research project at Cambridge, she would confide, ‘When I stood up to him … we had a first-class row … he has made me despise him so completely I shall be quite impervious to anything he may say in the future. He gave me an immense feeling of superiority in his presence.’
Sayre, who championed her friend, would admit that Franklin’s ogrish depiction of her professor was unkind and inaccurate. Professor Norrish was awarded the Nobel Prize in Chemistry in 1967.
Sayre had a correspondence with Norrish in which she described Franklin as ‘highly intelligent … and eager to make her way in scientific research’, but also ‘stubborn, difficult to supervise’ and, perhaps most tellingly, ‘not easy to collaborate with’. In Maddox’s opinion, ‘If Rosalind had wished, she could have twisted Wilkins around her little finger.’ The fact is she had no wish to collaborate with him. This left Wilkins isolated locally so instead he turned to Crick and Watson at Cambridge. It also meant that Franklin was equally isolated. To the commonsensical Crick, this may have been a crucial factor when it came to working out the molecular structure of DNA. ‘Our advantage was that we had evolved … fruitful methods of collaboration, something that was quite missing in the London group.’
In that same year of Franklin’s appointment, just before Wilkins headed for America, he asked his colleague, Alec Stokes – another Cambridge-educated physicist – if he could work out what kind of diffraction pattern a helical molecule of DNA would project onto an X-ray plate. It took Stokes just twenty-four hours to do the mathematics, largely figuring it out while travelling home on the commuter train to Welwyn Garden City. A helical model fitted very closely with the picture Gosling and Wilkins had obtained in their diffraction pictures of DNA. It would appear that if anybody first confirmed that DNA had a helical structure, the credits must surely include Wilkins, Gosling and Stokes – the latter would subsequently lament that, in retrospect, he might have merited 1/5000th of a Nobel Prize.
In November 1951, Wilkins told Watson and Crick that he now had convincing evidence that DNA had a helical structure. Watson had only recently heard Franklin say something similar in a talk about her research during a King’s College research meeting. This inspired Watson and Crick to attempt their first tentative three-dimensional model for DNA.
But where to begin?
Taking their cue from Linus Pauling, Watson and Crick decided that they would attempt to construct a three-dimensional physical model of the atoms and molecules that made up DNA with their covalent and hydrogen bond linkages to one another. On the face of it, the structure was made up of a very limited number of different molecules. There were the four nucleotides – guanine, adenine, cytosine and thymine – but they also knew that the structure contained a sugar molecule, deoxyribose, and a phosphate molecule. The phosphate was likely to be playing a structural role, perhaps holding the thread together, much as phosphate is a key structural component of our bony human spine. In the colloquium at King’s, attended by Watson, such was his lackadaisical absence of focus that he completely missed the importance of Franklin’s statement that the phosphate-sugar ‘spines’ were on the outside, with the coding nucleotides, the GACT, on the inside. As usual, he had eschewed making notes. All that seemed to intrigue Watson was the fact that the King’s people were uninterested in the model-building approach developed, with such aplomb, by Pauling.
In 1952 Franklin appears to have undergone a drastic change of heart in her own thoughts on the structure of DNA. She had in her possession a brilliantly clear X-ray picture of DNA, taken by Gosling, that clearly showed a helical structure to the molecule. She called this her ‘wet form’, and also her ‘B form’. But she had even clearer pictures of a different structure of the same molecule in its ‘dry form’, or ‘A form’, that did not appear to suggest a helix. The contrast between the two forms caused Franklin to dither as to whether the DNA molecule was helical. There is a suggestion that she may have asked the opinion of an experienced French colleague, who advised her to place her bets on whichever form gave the clearest pictures. She must have been altogether aware of the advice her ignored colleague, Wilkins, would have given. Unfortunately, she ended up putting the B form into a drawer, meanwhile focusing most of her research over that year into the A form.
Early that same year Watson and Crick made a first attempt at building a triple-stranded helical model of DNA, with a central phosphate-sugar spine. When Wilkins brought Franklin and Gosling up to Cambridge to view the model, they broke out into laughter. The model was absolute rubbish. It did not fit at all with the X-ray diffraction predictions. Thanks to Watson’s lackadaisical focus, and his failure to take notes at Franklin’s colloquium, he had made the cardinal error of putting the phosphate-sugar spine at the dead centre of their helix and not on the outside, as Franklin and Gosling had clearly deduced.
Sayre, who rightly defended Franklin from the egregious caricature depicted by Watson’s book, loses track of the contribution of Wilkins and Gosling. It is true that Franklin and Gosling had produced some of the clearest pictures yet of the B form of DNA, pictures of such clarity that they did come astonishingly close to the truth of its molecular structure. But then, confused for a year by the two seemingly different patterns of the A and B forms, Franklin veered away from her own earlier conclusions and for a year she took the view that DNA wasn’t helical at all. Sayre appears to refute this, but Gosling would subsequently confirm Wilkins’ account of how, on Friday 18 July 1952, Franklin goaded Wilkins with an invitation to a wake. The invitation card announced, with regret, the death of the DNA helix (crystalline) following a protracted illness. ‘It was hoped that Dr M. H. F. Wilkins would speak in memory of the deceased.’ At the time Wilkins assumed it was typical of Gosling’s sense of humour. But many years later he would discover that it was Franklin who had written the card, and it confirmed her refutation of any helical structure of DNA in that confused year.
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Frank Ryan
How could a relatively simple chemical code give rise to the complexity of a human being? How could our human genome have evolved? And how does it actually work?Over the past 50 years we have deciphered the inner workings of the human genome. From the basic structure of DNA through to the complete sequence of the code, what first appeared to be simple is actually a complex and beautiful three-dimensional world that makes each of us who we are.In The Mysterious World of the Human Genome acclaimed science writer Frank Ryan leads us through the most exciting scientific discoveries of the last 50 years, revealing how this science has unlocked the cure of some genetic diseases, developed the use of DNA in forensic science and paternity testing, helped us trace our ancestors and provided a definitive map for the movement of humans out of Africa. This scientific journey has had a profound impact on our understanding of the evolution of life itself, through the role of the most ancient of organisms in our basic biology all the way to the revelation that our most recent ancestor, Homo neanderthalensis, lives on in many of us.In the ever more complicated world of the human genome, this is the first book to explain how the human genome actually works as a whole and how that knowledge will have a profound effect on our understanding of where we have come from and where we are likely to be going in the future.
Copyright (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
William Collins
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This eBook first published in Great Britain by William Collins in 2015.
Text © FPR-Books Ltd 2015
Diagrams by Mark Salwowski
Frank Ryan asserts his moral right to be identified as the author of this work.
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Source ISBN: 9780007549061
eBook Edition © June 2015 ISBN: 9780007549078
Version: 2016-03-02
Dedication (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
To Oswald T. Avery
Possibly I am a scientist because I was curious when I was young. I can remember being ten, eleven, twelve years old and asking, ‘Now why is that? Why do I see such a peculiar phenomenon? I would like to understand that.’
LINUS PAULING
Table of Contents
Cover (#u3af8175c-f258-5aef-b829-c7a1ebaacaf9)
Title Page (#ub5818fc8-1cfc-5065-b3d3-5c502ebf4ddd)
Copyright (#ue1d03a02-d5fb-5bb0-bc5e-8a44f220831e)
Dedication (#uad5cd499-705e-5b89-8db7-4bf4bdb35f4c)
Epigraph (#u4d5d602f-7992-5f18-b605-bfe44bdd4227)
Introduction (#u2416afec-85a4-5d0c-8645-3951116e978d)
Chapter One: Who Could Have Guessed It? (#u05e980ed-4d22-5d4a-8297-9b81da3b9238)
Chapter Two: Dna Is Confirmed as the Code (#u888a0706-a215-5ddb-b81a-cf7ffb4bafe5)
Chapter Three: The Story in the Picture (#ub36631bd-86c2-521b-aaeb-2af0e5d50298)
Chapter Four: A Couple of Misfits (#u81b62540-240a-52ea-91b6-64747f7b3270)
Chapter Five: The Secret of Life (#u4e6ea3b3-7aa6-5680-ae66-ab331263e1d9)
Chapter Six: The Sister Molecule (#litres_trial_promo)
Chapter Seven: The Logical Next Step (#litres_trial_promo)
Chapter Eight: First Draft of the Human Genome (#litres_trial_promo)
Chapter Nine: How Heredity Changes (#litres_trial_promo)
Chapter Ten: The Advantage of Living Together (#litres_trial_promo)
Chapter Eleven: The Viruses That Are Part of Us (#litres_trial_promo)
Chapter Twelve: Genomic Level Evolution (#litres_trial_promo)
Chapter Thirteen: The Master Controllers (#litres_trial_promo)
Chapter Fourteen: Our History Preserved in Our Dna (#litres_trial_promo)
Chapter Fifteen: Our More Distant Ancestors (#litres_trial_promo)
Chapter Sixteen: The Great Wilderness of Prehistory (#litres_trial_promo)
Chapter Seventeen: Our Human Relatives (#litres_trial_promo)
Chapter Eighteen: The Fate of the Neanderthals (#litres_trial_promo)
Chapter Nineteen: What Makes You Unique (#litres_trial_promo)
Chapter Twenty: The Fifth Element (#litres_trial_promo)
Bibliography (#litres_trial_promo)
Chapter Notes (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
By the Same Author (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
Introduction (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
No special act of creation, no spark of life was needed to turn dead matter into living things. The same atoms compose them both, arranged only in a different architecture.
JACOB BRONOWSKI,THE IDENTITY OF MAN
Bronowski begins his more famous book, The Ascent of Man, with the words, ‘Man is a singular creature. He has a set of gifts which make him unique among the animals: so that, unlike them, he is not a figure in the landscape – he is a shaper of the landscape.’ But why should we humans have become shapers of the landscape rather than mere figures inhabiting it? We differ from, say, a sea horse or a cheetah because our genetic inheritance, the sum of the DNA that codes for us, is different in humans when compared to the horse or the cheetah. We call this the genome, or, to be more specific in our case, the human genome.
Our genome defines us at the most profound level. That same genome is present in every one of the approximately 100,000 billion cells that make us who we are as individual members of the human species. But it runs deeper than that. In more personal terms, in myriad tiny variations that we each possess and are individual to us only, it is the very essence of us, all that, in genetic and hereditary terms, we have to contribute to our offspring, and through them to the sum total evolutionary inheritance of our species. To understand it is to know, in the most intimate sense, what it means to be human. No two people in the world today have exactly the same genome. Even identical twins, who will have been conceived with exactly the same genome, will have developed tiny differences between their genomes by the time of their births: differences that may have arisen in parts of their genomes that don’t actually code for what we normally mean by genes.
How strange to realise that there is actually more to our individual genome than genes alone. But let us put aside such details for the moment to focus on the more general theme. How could a relatively simple chemical code give rise to the complexity of a human being? How could our human genome have evolved? How does it actually work? Immediately we are confronted by mysteries.
To answer these questions we need to explore the genome’s basic structure, its operating systems and its mechanisms of expression and control. Some readers might react with incredulity. Surely any such exploration promises a journey into extraordinary complexity, one that is far too obscure and scientific for a non-scientist reader? In fact this book is aimed at exactly such a reader. As we shall see, the basic facts are easy enough to grasp, and the way to grasp them is to break the exploration into a series of simple, and eminently logical, stages. This journey will lead us through a sequence of remarkable revelations about our human history – even into the very distant past of our ancestors’ lives and their prehistoric exploration of our beautiful life-giving planet.
The exploration will raise other, equally important, questions, too. How, for example, does this extraordinary entity that we call the human genome enable our human reproduction – the fertilisation of our maternal egg with the paternal sperm? How does it control the quasi-miracle of the developing embryo within the mother’s womb? Returning to generalities for the moment, though, we can be sure that an important ingredient of the genome, and its essential nature, is memory – the memory, for example, of the totality of every individual human’s genetic inheritance. But how exactly does it perform this remarkable feat of memory? We know already that this wonder chemical we call DNA works like a code, but how could any code recall the complex instructions that go into the making of cells and tissues and organs, and then once made, bring them into function in the single coordinated whole that comprises the human being? Even then we have hardly begun to confront the mysteries of the human genome. How does this same extraordinary structure acquire the programming that gifts the growing child with the wonder of speech, that bestows the related capacity for learning, writing and education, and which makes possible the maturing of the newborn to the future adult, who then repeats the cycle all over again when he or she becomes a parent in turn?
The wonder is that all of this might be encompassed in a minuscule cluster of chemicals including, but not exclusive to, the master molecule we call deoxyribonucleic acid – or DNA. This chemical code somehow records the genetic instructions for making us. Built into that code must be the potential for individual liberty of thought and inventiveness, enabling every human artistic, mathematical and scientific creativity. It gives rise to what each of us thinks innately as our private inviolate ‘self’. Somehow that same construction of ‘self’ made possible the genius of Mozart, Picasso, Newton and Einstein. It is little wonder that we look at the repository of such potential with awe. No more is it surprising that we should want to understand this mystery that lies at the very core of our being.
Only recently have we come to understand the human genome in sufficient depth and subtlety to be able to put together its marvellous story – to discover, for example, that there is rather more to it than DNA alone. This is the story I shall attempt to convey in this book.
A few years ago I gave a lecture on a related theme at King’s College London. The chairman asked me if I planned to write a book about it. When I said yes, he asked me to please write it in words that a lay reader, like himself, could readily understand.
‘Just how simple do you want me to make it?’
‘I want you to assume that I – your reader – know nothing at all to begin with.’
This, then, I promise to do. There will be no complicated scientific language, no mathematical or chemical formulae or unexplained jargon, and I shall introduce no more than a handful of simple illustrations. Instead I shall begin from first principles and assume that the readers of this book know little about biology or genetics. Even non-biologists might recall the many surprises when the first rough draft of the human genome was announced to the world, in 2001.The discoveries since then have confirmed that a good deal of the human genome – in its evolution, structure and workings – is far from what we had earlier imagined. Those surprises do not diminish the importance of the wealth of knowledge that had gone before, but rather, like all great scientific discoveries, they enhance it. Thanks to this new understanding, humanity has entered what I believe to be a golden age of genetic and genomic enlightenment, which is already being extrapolated to many important fields, from medicine to our human prehistory. I think society at large deserves to understand this and what it promises for the future.
one (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
Who Could Have Guessed It? (#u3cc4e59e-fbac-50eb-b189-73362bd481d1)
The large and important and very much discussed question is: How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?
ERWIN SCHRÖDINGER
In April 1927 a young Frenchman, René Jules Dubos, arrived at the Rockefeller Institute for Medical Research, in New York, on what would appear to have been a hopeless mission. Tall, bespectacled and a recent graduate of Rutgers University, New Jersey, with a PhD in soil microbiology, Dubos had an unusually philosophical attitude to science. He had become convinced, through the work of eminent Russian soil microbiologist Sergei Winogradsky, that it was a waste of time studying bacteria in test tubes and laboratory cultures. Dubos believed that if we really wanted to understand bacteria we should go out and study them where they actually lived and interacted with one another and with life in general, in the fields and the woods – in nature.
On graduation from Rutgers Dubos had found himself unemployed. He had applied to the National Research Council Fellowship for a research grant but had been turned down because he wasn’t American, but somebody had scribbled a handwritten message on the margin of the rejection letter. Dubos would later reflect upon the fact that it was written in a female hand, almost certainly added as a kindly afterthought by the official’s secretary. ‘Why don’t you go and ask advice and help from your famous fellow countryman, Dr Alexis Carrel, at the Rockefeller Institute?’ Dubos duly wrote to Carrel, which brought him, in April 1927, to the building on York Avenue, on the bank of the East River.
Dubos knew nothing about Carrel, or indeed about the Rockefeller Institute for Medical Research, and was surprised on his arrival to discover that Carrel was a vascular surgeon. Dubos had no academic knowledge of medicine and Carrel knew nothing about the microbes that lived in soil. The outcome of their conversation was all too predictable; Carrel was unable to help the youthful microbiologist. Their conversation closed about lunchtime and Carrel did Dubos the courtesy of inviting him to have lunch with him in the Institute’s dining room, which had the attraction for a hungry Frenchman that they served freshly baked bread.
It seemed entirely by accident that Dubos found himself sitting at a table next to a small, slightly built gentleman with a domed bald head who addressed him politely in a Canadian accent. The gentleman’s name was Oswald Theodore Avery. Although Dubos later confessed that he knew as little about Avery as he did of Carrel, Professor Avery (his close associates referred to him as ‘Fess’) was eminent in his field, which was medical microbiology. It would prove to be a meeting of historic importance both to biology and to medicine.
Avery subsequently hired Dubos as a research assistant, in which role Dubos discovered the first soil-derived antibiotics. Meanwhile Avery led his small team – who were working on what he called his ‘little kitchen chemistry’ – on another quite different quest, one that would help unravel the key to heredity. Why then does society know little to nothing about this visionary scientist? To understand how this anomaly came about we need to go back in time to the man himself and the problems he faced three-quarters of a century ago.
*
In 1927, when Dubos first met Avery, the principles of heredity were poorly understood. The term ‘gene’ had been introduced into the nomenclature two decades earlier by a Danish geneticist, Wilhelm Johannsen. Curiously, Johannsen had adopted a vague concept of heredity, known as ‘pangene’, that was first proposed by Charles Darwin himself. Johannsen modified it to take on board the belated discovery of the pioneering work of Gregor Mendel, which dated back to the nineteenth century.
Readers may be familiar with the story of Mendel – the cigar-smoking, Friar-Tuck-like abbot of an Augustinian monastery in Brünn, Moravia (now the Czech Republic) – who undertook some brilliantly original studies of the peas he cross-bred in the monastery vegetable garden. From these studies Mendel discovered the basis of what we now know as the laws of heredity. He found that certain characteristics of the peas were transmitted to the offspring in a predictable manner. These characteristics included tallness or dwarfishness, presence or absence of the colours yellow or green in the blossoms or axils of the leaves, and the wrinkled or smooth skin in the peas. Mendel’s breakthrough was to realise that heredity was stored within the germ cells of plants – and this would subsequently be extrapolated to all living organisms – in the form of discrete packets of information that somehow coded for specific physical characters or ‘traits’. Johannsen coined the term ‘gene’ for Mendel’s packet of hereditary information. At much the same time, a combative British researcher, William Bateson, extrapolated the term ‘gene’ to the discipline he now called ‘genetics’ to cover the study of the nature and workings of heredity.
Today, if we visit the free dictionary online, we get the following definition of a gene: ‘The basic physical unit of heredity; a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for the synthesis of RNA, which, when translated into protein, leads to the expression of hereditary character.’ But Mendel had no notion of genes as such, and he certainly knew nothing about DNA. His discoveries languished in some little-read papers for forty years before they were rediscovered and their importance was more fully understood. But in time his idea about the discrete packets of heredity we now call genes helped to answer a very important medical mystery: how certain diseases come about through an aberration of heredity.
We now know that genes are the basic building blocks of heredity in much the same way that atoms are the physical units that make up the physical world. But during the early decades of the twentieth century, nobody had any real notion of what genes were made from, or how they worked. But here and there, people began to study genes in more depth by examining their physical expression during the formation of embryos or in the causation of hereditary diseases. Fruit flies became the experimental model for pioneering research in the laboratory of Chicago-based geneticist Thomas Hunt Morgan, where researchers located genes, one by one, onto structures called chromosomes, which were themselves located within the nuclei of the insect’s germ cells. The botanical geneticist Barbara McClintock confirmed that this was also the case for plants. McClintock developed techniques that allowed biologists to visualise the actual chromosomes in maize, leading to the groundbreaking discovery that, during the formation of the male and female germ cells, the matching, or ‘homologous’, chromosomes from the two parents lined up opposite each other and then the chromosomes swapped similar bits so that the offspring inherited a jumbled-up mixture of the inheritance from the two parents. This curious genetic behaviour (which is known as ‘homologous sexual recombination’) is the explanation of why siblings are different from one another.
By the early 1930s biologists and medical researchers knew that genes were actual physical entities – chemical blocks of information that were lined up like beads in a necklace along the lengths of chromosomes. In other words, the genome could be loosely compared to a library of chemical information in which the books were the chromosomes. The discrete entities known as genes could then be compared to discrete words in the books. The libraries were housed in the nuclei of the germ cells – in human terms, the ova and sperm. Humans had a total stack of 46 books, which were the summed complement of ova and sperm, in every living cell. This came about because the germ cells – the ovum and the sperm – contained 23 chromosomes, so that when a human baby was conceived the two sets of the parental chromosomes united within the fertilised ovum, passing on the full complement of 46 chromosomes to the offspring. But this initial unravelling of the ‘heredity mystery’ merely opened up a Pandora’s box of new mysteries when it came to applying genetics to the huge diversity of life on our fecund planet.
For example, did every life form, from worms to eagles, from the protozoa that crawled about in the scum of ponds to humanity itself, carry the same kinds of genes in their nuclei-bound chromosomes?
The microscopic cellular life forms, including bacteria and archaea, do not store their heredity in a nucleus. These are called the ‘prokaryotes’, which means pre-nucleates. All other life forms store their heredity in nuclei and are known collectively as ‘eukaryotes’, which means true nucleates. From the growing discoveries in fruit flies, plants and medical sciences, it was becoming rather likely – excitingly so – that some profound commonalities might be found in all nucleated life forms. But did the same genetic concepts, such as genes, apply to the prokaryotes, which reproduced asexually by budding, without the need for germ cells? At this time within the world of early bacteriology there was even a debate as to whether bacteria should be seen as life forms at all. And viruses, which were for the most part several orders of magnitude smaller than bacteria, were little understood.
Over time many researchers came to see bacteria as living organisms, classifying them according to the binomial Linnaean system; so, for example, the tuberculosis germ was labelled Mycobacterium tuberculosis and the boil-causing coccoid germ was labelled Staphylococcus aureus. Oswald Avery, with his extremely conservative nature, kept his options open, eschewing the binomial system and referring to the TB germ as the ‘tubercle bacillus’. It is instructive for our story that Dubos, who came to know Avery better than any other colleague, would observe that ‘Fess’ was similarly conservative in his approach to laboratory research. Science must adhere with a puritanical stringency to what can be logically observed and definitively proven in the laboratory.
In 1882 German physician Robert Koch discovered that Mycobacterium tuberculosis was the cause of the greatest infectious killer in human history – tuberculosis. Koch constructed a code of logic that would be applied to bugs when first determining if they caused specific diseases. Known as ‘Koch’s postulates’, this was universally adhered to, and once a causative bug had been identified it was studied further under the microscope. Thus the bug was duly classified in a number of ways. If its cells were rounded in shape it was a ‘coccus’, if a sausage shape it was a ‘bacillus’, if a spiral shape it was a ‘spirochaete’. Bacteriologists methodically studied the sort of culture media in which a bug would grow best – whether in agar alone, or agar with added ox blood, and so on. They also studied the appearance of the bacterial colonies when they were grown in culture plates – their colours, the size of the colonies, whether they were rough in outline or round and smooth, raised or flat, stellate, granular or daisy-head. So the textbooks of bacteriology extended their knowledge base on a foundation of precise factual study and observation. And as understanding grew, this newfound knowledge was applied to the war against infection.
One of the useful things they learnt about disease-causing, or ‘pathogenic’, bacteria was that the behaviour of the disease, and thus of the bug itself in relation to its infected host, could be altered by various deliberate means: for example, through repeated cultures in the laboratory, or by repeatedly passing generations of the bug through a series of experimental animals. Through such manipulations it was possible to make the disease worse or less severe by making the bug either ‘more virulent’ or ‘attenuated’. Bacteriologists looked for ways to extrapolate this to medicine. In France, for example, the eminent Louis Pasteur used this principle of attenuation to develop the first vaccine to be used successfully against the otherwise universally fatal virus infection of rabies.
One fascinating observation that came out of these studies was the fact that, once a bug had been attenuated or been driven to greater virulence, the change in behaviour could be ‘passed on’ to future generations. Could it be that some factor of the bug’s own heredity had been altered to explain the change in behaviour?
Bacteriologists talked about ‘adaptation’, using the same term that was coming into vogue with evolutionary biologists when referring to evolutionary change in living organisms as they adapted to their ecology over time. While it was too early to be sure if bacterial heredity depended on genes, these scientists linked it to the physical appearance of bugs and colonies, or to the bugs’ internal chemistry, and even to their behaviour in relation to their hosts. These were measurable properties, the bacterial equivalents of what evolutionary biologists were calling the ‘phenotype’ – the physical make-up of an organism as opposed to what was determined by the hereditary make-up, or ‘genotype’.
Bacteriologists also came to recognise that the same bacterium could exist in different subtypes, which could often be distinguished from one another using antibodies. These subtypes were called ‘serotypes’. In 1921 a British bacteriologist, J. A. Arkwright, noticed that the colonies of a virulent type of dysentery bug, called Shigella, growing on the jelly-coated surfaces of culture plates, were dome-shaped with a smooth surface, whereas colonies of an attenuated, non-virulent, type of dysentery bug were irregular, rough-looking and much flatter. He introduced the terms ‘Smooth’ and ‘Rough’ (abbreviated to S and R) to describe these colonial characteristics. Arkwright recognised that the ‘R’ forms cropped up in cultures grown under artificial conditions, but not in circumstances where bacteria were taken from infected human tissues. He concluded that what he was observing was a form of Darwinian evolution at work.
In his words: ‘The human body infected with dysentery may be considered a selective environment which keeps such pathogenic bacteria in the forms in which they are usually encountered.’
Soon researchers in different countries confirmed that loss of virulence in a number of pathogenic bacteria was accompanied by the same change in colony appearance from Smooth to Rough. In 1923, Frederick Griffith, an epidemiologist working for the Ministry of Health in London, reported that pneumococci – the bugs that caused epidemic pneumonia and meningitis which were of particular interest to Oswald Avery at the Rockefeller Laboratory – formed similar patterns of S and R forms on culture plates. Griffith was known to be a diligent scientist and Avery was naturally intrigued.
Griffith’s experiments also produced an additional finding, one that really shook and puzzled Avery.
When Griffith injected non-virulent R-type pneumococci from the strain known as type I into experimental mice, he included an additional ingredient in the injections, a so-called ‘adjuvant’, which usually pepped up the immune response to the R pneumococci. A common adjuvant for these purposes was mucus taken from the lining of the experimental animal stomach. But for some obscure reason Griffith switched adjuvant to a suspension of S pneumococci, derived from type II, that had been deliberately killed off by heat. The experimental mice died from overwhelming infection. In the blood of these dead mice Griffith expected to find large numbers of multiplying R-type I bacteria – the type that he had injected at the start of the experiment. Why then had he actually found S-type II? How on earth could adding dead bacteria to his inoculum have changed the actual serotype of the bacterium from non-virulent R-type I to highly virulent S-type II?
Researchers, including Avery himself, had previously shown that S and R types were determined by differences in the polysaccharide capsules coating the cell bodies of the bugs. Griffith’s findings suggested that the test bacteria, initially R-type pneumococci, had changed their polysaccharide coats inside the infected bodies of the mice to that of the virulent strain. But they could not have achieved this by just flinging off the old coat and putting on the new one. The coat was determined by the bacteria’s heredity – it was an inherited characteristic. Further cultures of the recovered bacteria confirmed that the S type bred true. There appeared to be only one possible explanation: adding the dead S bacteria to the living R bacteria had induced a mutation in the heredity of the living R-type bacteria, so they literally transformed into S-type II.
In the words of Dubos: ‘[At the time] Griffith took it for granted that the changes remained within the limits of the species. He probably had not envisaged that one pneumococcus type could be transformed into another, as this was then regarded as the equivalent of transforming one species into another – a phenomenon never previously observed.’
*
It is little wonder that Avery was astonished by Griffith’s findings. Like Robert Koch before him, Avery subscribed to the view that bacterial strains were immutable in terms of their heredity. The very concept of a mutation – that heredity was capable of an experimentally induced change – was a highly controversial issue within biology and medicine at this time. To understand why, we need to grasp the concept of what a mutation means.
By the late nineteenth century Darwinian theory had entered a crisis. Darwin himself had been well aware that natural selection relied on some additional mechanism, or mechanisms, capable of changing heredity, so that natural selection would have a range of ‘hereditable variation’ to choose between. Generations later, in the opening chapters of his innovative book Evolution: The Modern Synthesis,Julian Huxley put his finger on the nub of the problem. ‘The really important criticisms have fallen upon Natural Selection as an evolutionary principle and centred round the nature of inheritable variation.’ In 1900, a Dutch biologist, Hugo de Vries, put forward a novel mechanism that would be capable of providing the necessary variation: the concept of a random change in a unit of inheritance. Opportunity for change exists when genes are copied during reproduction, when a random change in the coding of a gene might arise from an error in copying the hereditary information. De Vries called this source of hereditary change a ‘mutation’. It was only with what Julian Huxley termed ‘the synthesis’ of Mendelian genetics – the potential for change in the inherited genes through mutation – and Darwinian natural selection operating on the hereditary choices presented within a species, that Darwinian theory became credible again to the great majority of scientists.
In time Griffith’s finding would be confirmed to be what Avery was now wondering about: it was a mutation. Geneticists would show that the change from the R to the S strain of pneumococcus involved the transfer of a gene from the dead S-type II bacteria to the living R-type I bacteria, which was incorporated into subsequent bacterial reproductive cycles, transforming the cells of the R-type I bacterium into the cells of the S-type II bacterium. It was indeed the bacterial equivalent of a change of species. And Griffith was proven right in inferring that Darwinian natural selection had operated even in the short time frame of the infection of a cohort of laboratory mice.
Griffith’s experimental findings galvanised bacteriologists and immunologists around the world. His discovery was confirmed in several different research centres, including the Robert Koch Institute in Berlin, where the pneumococcal types had first been classified. The news was inevitably a hot topic of discussion in Avery’s department, as Dubos would recount: ‘but we did not even try to repeat them at first, as if we had been stunned and almost paralysed intellectually by the shocking nature of the findings’.
At first Avery simply couldn’t believe that bacterial types could be transformed. Indeed, he had been one of the authoritative figures who had settled the fixity of bacterial reproduction being true to type years before. But from 1926 Avery encouraged a young Canadian physician working in the Rockefeller Laboratory, M. H. Dawson, to investigate the situation. According to Dubos, Dawson, unlike Avery, was convinced from the start that Griffith’s conclusion must be correct because he believed that ‘work done in the British Ministry of Health had to be right’.
Dawson began by confirming Griffith’s findings in laboratory mice. His results suggested that the majority of non-virulent bacteria – the R types – had the ability in certain circumstances to revert to the virulent S type. By 1930 the young Canadian was joined by a Chinese colleague, Richard P. Sia, and between them they took the experimental observations further by confirming that the hereditary transformation could be brought about in culture media, without the need for passage through mice. At this stage, Dawson left the department and Avery encouraged another young physician, J. L. Alloway, to take the investigation further. Alloway discovered that all he needed to bring about the transformation was a soluble fraction derived from the S pneumococci by dissolving the living cells in sodium deoxycholate, then passing the resultant solution through filters to remove the bits of broken-up cells. When he added alcohol to the filtered solution, the active material precipitated out as sticky syrup. Throughout the laboratory this sticky syrup was referred to as the ‘transforming principle’. So the work continued, experiment following experiment, year by year.
When Alloway left the department, in 1932, Avery began to devote some of his own time to the pneumococcus transformation, in particular aiming to improve the extraction and preparation of the transforming substance. Frustration followed frustration. He focused on its chemical nature. Discussion took place with other members of the department, ranging from the ‘plamagene’ that was thought to induce cancer in chickens (now known to be a retrovirus), or to the genetic alterations in bacteria that were thought to be caused by viruses. According to Dubos, Alloway suggested the transforming agent might be a protein-polysaccharide complex. But by 1935 Avery was beginning to think along other lines. In his annual departmental report that year he indicated that he had obtained the transforming material in a form that was essentially clear of any capsular polysaccharide. In 1936, Rollin Hotchkiss, a biochemist who had now arrived to work in the department, wrote a historic comment in his personal notes:
‘Avery outlined to me that the transforming agent could hardly be a carbohydrate, did not match very well with a protein and wistfully suggested it might be a nucleic acid!’ At this stage, Dubos, who many years later would write a book about Avery and his work, dismissed this as no more than a surmise. There were good reasons for his caution.
That year few researchers throughout the world believed that the answer to heredity lay with nucleic acids. These chemical entities had been discovered by a Swiss biochemist, Johann Friedrich Miescher, back in the late 1800s. Fascinated by the chemistry of the nucleus, Miescher had broken open the nuclei of white blood cells in pus, and subsequently the heads of salmon sperm, to discover a new chemical compound which was acidic to pH testing, rich in phosphorus and comprised of enormously large molecules. After a lifetime of experimentation on the discovery, Miescher’s pupil, Richard Altmann, would introduce the term nucleic acid to describe Miescher’s discovery. By the 1920s, biochemists and geneticists were aware that there were two kinds of nucleic acids. One was called ribonucleic acid, or RNA, which contained four structural chemicals: guanine, adenine, cytosine and uracil, or GACU. The other was called ‘desoxyribonucleic acid’, or DNA, which was a major component of the chromosomes. They had deciphered its four bases – three identical to RNA, guanine, adenine and cytosine, but with the uracil replaced by thymine – making the acronym GACT. They knew that these four bases consisted of two different pairs of organic chemicals; adenine and guanine being purines, and cytosine and thymine being pyrimidines. They also knew that they were strung together to form very long molecules. At first they thought that RNA was confined to plants while DNA was confined to animals, but by the early thirties this was dismissed when it was found that both RNA and DNA were universally distributed throughout the animal and plant kingdoms. Still they had no knowledge of what nucleic acids actually did in the nuclei of cells.
A distinguished organic chemist based at the Rockefeller Institute, Phoebus Aaron Levene, proposed that the structures of DNA and RNA were exceedingly boring – they formed groups of four bases that repeated themselves in the identical repetitive formation throughout the molecule, like a four-letter word, repeated ad nauseam. This was called ‘the tetranucleotide hypothesis’. Such a banal molecule couldn’t possibly underlie the exceedingly complex basis of heredity. In the words of Horace Freeland Judson, ‘the belief was held with dogmatic tenacity that DNA could only be some sort of structural stiffening, the laundry cardboard in the shirt, the wooden stretcher behind the Rembrandt, since the genetic material would have to be protein’.
Proteins are lengthy molecules made up of smaller organic chemical units known as amino acids. There are 20 amino acids in the make-up of proteins, reminiscent of the number of letters that make up alphabets. If genes were the hereditary equivalents of words, only the complexity of proteins could fashion the words capable of spelling out the narratives. Chemists, and through extrapolation geneticists, not unnaturally assumed that only this level of complexity could possibly accommodate the incredible memory template that the complexity of heredity demanded – a line of thought that Judson labelled ‘The Protein Version of the Central Dogma’.
This was the contentious zeitgeist that Avery now confronted. As early as 1935, in his annual reports to the Board of the Institute, he indicated that he had growing evidence that the ‘transforming substance’ appeared free of capsular polysaccharide and it did not appear to be a protein.
Further progress on this line of research appeared to drag. In part this was because Dubos, working in the same department, had made a breakthrough in his search for antibiotic drugs. In 1925, Alexander Fleming, at St Mary’s Hospital in London, had discovered a potential antibiotic, penicillin, but he had been unable to take his work to the stage of useful production for medical purposes. Now, working on the philosophical principle encapsulated by the biblical saying ‘dust to dust’, Dubos had pioneered the search for microbes in soil that would potentially attack the polysaccharide coat of the pneumococcus. By the early 1930s he was making progress. From a cranberry bog in New Jersey he found a bacillus that dissolved the thick polysaccharide capsule that coated the pneumococcus with its armour-like outer covering. Dubos went on to extract the enzyme that the Cranberry Bog bacillus produced. He and Avery had reported their discovery in a paper in the journal, Science, in 1930. In a further series of papers the two scientists would report further experiments, all aimed at extrapolating the discovery to human trials of the Cranberry Bog enzyme in treating the potentially fatal pneumonia and meningitis caused by the pneumococcus.
But their researches encountered difficulty after difficulty. In part these arose from a predictable ignorance in a field of such pioneering research. A more personal, and devastating, problem arose when, under the stress of it all, Avery developed thyrotoxicosis – a debilitating autoimmune illness in which his thyroid gland became overactive.
Thyrotoxicosis causes the system to be flooded by thyroid hormones, which would have inappropriately switched his metabolism into a dangerous overdrive. He would have felt shaky, agitated, physically and mentally restless, suffering difficulties with relaxation and sleep – an impossible situation for a creative person. Avery had to spend time away from the lab undergoing surgery to remove the bulk of the ‘toxic goitre’, a procedure that carried risk of side-effects, even fatality in a minority of cases. His surgeon advised him against any early activity, physical or mental, that provoked stress. Dubos later recalled how Avery was away from his work for as long as six months. And while Avery was away, the laboratory stagnated. In Dubos’ own words, ‘I … pursued [the research] for three or four years. However I could not carry the work very far because there were serious gaps in both my knowledge of genetics and biochemistry and in the [prevailing] states of these sciences themselves.’
Dubos would continue his researches against such difficulties, to be rewarded, in 1939, with the discovery of the first soil-derived antibiotic. He called it ‘gramicidin’. But gramicidin could not be taken by mouth or administered by injection because it was too toxic. It could only be applied to skin conditions. The research continued. But then, all of a sudden, the hopes of Avery and Dubos were overtaken by a rival breakthrough. Working in the pharmaceutical research laboratories of the Bayer Company in Elberfeld, Germany, doctor Gerhard Domagk reported the discovery of a new antibacterial agent called prontosil. The first of what would come to be known as the sulphonamide drugs, it immediately entered the medical formulary, pioneering the treatment of a number of hitherto untreatable infectious diseases.
Today we are apt to forget how little we could do to control infection in the 1930s. Epidemics such as scarlet fever, measles, pneumonia, meningitis and poliomyelitis swept through the population in regular, sometimes annual, cycles. Other notorious infections were everyday threats, including tuberculosis, which ravaged entire families, or boils, septic arthritis, septic osteomyelitis, which caused agonising abscesses in bone, and the commonplace but potentially deadly streptococci capable of breaking through a septic throat to cause abscesses in the brain. Most of the human population, whether in developed or developing countries, died from infections, including the insidious pneumonias that hit those whose immunity was depressed. The treatment of infections was the most urgent problem then facing humanity. For Dubos, and even more so Avery, the disappointment of failing in their line of research would have been shattering.
When, in due course, Avery returned to work, he switched the emphasis of his research to the ‘transforming substance’. Colin MacLeod improved the techniques of extraction so they could now produce sizeable amounts for assay and further testing. They began to make more rapid progress so that, in a report to the Rockefeller Board for the year 1940–41, they were more confident in stating that even a highly purified extract of the transforming substance appeared to be protein-free.
That summer MacLeod left the Institute to become Professor of Bacteriology at the New York University School of Medicine. But he still took an interest in the project and frequently returned to the Institute to add his advice. A young paediatrician, Maclyn McCarty, took MacLeod’s place in the transforming experiment. McCarty brought a useful level of biochemical training to the laboratory. And now they had the transforming substance in quantity and in stable form, he applied his chemical skills to further process and identify the active material. He began to culture the pneumococci in large batches of 50 to 75 litres, developing a series of steps that increased the yield of transforming substance while removing proteins, polysaccharides and ribonucleic acid. The prevailing beliefs about the hereditary principle claimed that nucleoproteins were the answer. Thus the topmost priority in all of this effort was to ensure that the final test material contained no protein.
By now McCarty had extracted concentrated solutions of the active material. He treated this with a series of protein-digesting enzymes, such as the gut-derived trypsin and chymotrypsin, which were known to destroy proteins, ribonucleic acid and pneumococcal capsular polysaccharide. What remained was once more shaken with chloroform in a final effort to remove even the finest traces of protein.
By late 1942, after repeated extraction and experiment, McCarty had come to the conclusion that the transforming activity was confined to a highly viscous fraction that consisted almost exclusively of polymerised deoxyribonucleic acid. When he precipitated this fraction in a flask by adding absolute ethyl alcohol, drop by drop, all the while stirring the solution with a glass rod, the active material separated out of the solution in the form of long, white and extremely fine fibrous strands that wound themselves around the stirring rod. Dubos would recall the excitement felt within the lab by all those who witnessed the sight of the beautiful fibres, which were the pure form of the transforming substance.
In early 1943, Avery, MacLeod and McCarty presented their findings to distinguished chemists at the Princeton section of the Rockefeller Institute for Medical Research. The chemists must have been astonished, perhaps even nonplussed, but they offered no contradiction of the evidence nor asked for further proof. The researchers summed up the evidence for the Board of the Rockefeller in April of that year. Avery, MacLeod and McCarty, all three medical doctors rather than geneticists, were now ready to inform the world in a paper submitted to the Journal of Experimental Medicine in November the same year, which would be published early the following year. The title of the paper was long-winded and cautious: ‘Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Induction of transformation by a desoxyribonucleic acid fraction isolated from pneumococcus type III’.
In the words of Dubos, this paper ‘had staggering implications’. The sense of excitement, tempered by caution, was captured in a letter that Avery wrote to his brother, Roy, dated 26 May 1943:
… For the past two years, first with MacLeod and now with Dr McCarty, I have been trying to find out what is the chemical nature of the substance in the bacterial extracts which induces this specific change … Some job – and full of heartaches and heartbreaks. But at last perhaps we have it … In short, the substance … conforms very closely to the theoretical values of pure desoxyribose nucleic acid. Who could have guessed it?
In the letter, ‘desoxyribose nucleic acid’, in the paper, ‘desoxyribonucleic acid’: these are older names for what we now call deoxyribonucleic acid – commonly reduced to its acronym, DNA.
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DNA Is Confirmed as the Code (#ulink_a8f9dc67-6bfa-5215-bbf6-a95d6a68aef6)
Looking back at his own failure to appreciate Avery’s discovery at the time, Stent came to the conclusion ‘in some respects Avery et al’s paper is a more dramatic example of prematurity than Mendel’s’.
UTI DEICHMANN
Scientists, in the opinion of the Nobel Prize-winning Linus Pauling, were fortunate because their world was so much the richer for its mysteries than those not interested in science could possibly appreciate. Certainly in those days Avery’s lab at the Rockefeller Medical Institute for Research was filled with a mood of expectation and excitement. In 1943 Oswald Avery was 65 years old. He had planned to retire and join his brother Roy’s family in Nashville, Tennessee, but there was no question of his leaving the lab at this time. He needed to continue his work on the transforming substance. In particular he needed to convince his colleagues throughout the world of microbiology and, more widely, the sceptical world of biochemists and geneticists, of the validity of their discovery.
Avery was conservative by nature. A generation earlier he and a colleague had proposed that complex sugar molecules, called polysaccharides, and not proteins determined the immunological differences between different types of pneumococcal bacteria. Although this theory was eventually confirmed to be true, at the time of discovery it provoked a storm of controversy that had haunted this nervous and sensitive man. In a long and rambling letter to his brother Avery had repeatedly referred to his worry about the reaction to the new discovery. ‘It’s hazardous to go off half-cocked … It’s lots of fun to blow bubbles – but it’s wiser to prick them yourself before someone else tries to.’
Avery had an adversary closer to home. Alfred E. Mirsky, a distinguished biochemist and geneticist also working at the Rockefeller Institute, had reacted to Avery’s discovery with incredulity. To make matters worse, Mirsky was widely regarded as an expert on DNA. He had discovered that the quantity of DNA in every cell nucleus remained the same, establishing a principle called ‘DNA constancy’. He now doubted the efficacy of McCarty’s DNA extraction. A stickler for ‘clean’ biochemical experiment, Mirsky believed that protein found in the nucleus, called nucleoprotein, must be the basis of heredity. Even as late as 1946, Mirsky insisted that the two enzymes McCarty had used in his extractions would not digest away all of the protein. Mirsky was very influential in genetic circles and his argument impressed the leading geneticist of the time, Hermann J. Muller, who had been awarded the Nobel Prize that same year for his discovery, made two decades earlier, that X-rays caused mutations in the genes of the fruit fly. In a letter to a geneticist colleague, Muller stated ‘Avery’s so-called nucleic acid is probably nucleoprotein after all, with the protein too tightly bound to be detected by ordinary method.’
To some extent such disagreement was typical of the situation one might find anywhere in science when various groups from different scientific backgrounds are investigating a major unknown. Never is the argument more acrimonious than when a new discovery confounds the accepted paradigm. But the vociferous opposition of Mirsky from within Avery’s home research foundation must have been particularly damaging. In 1947 Muller published his ‘Pilgrim’s Lecture’ as a scientific paper in which he concluded that whether nucleic acid or protein was the answer ‘must as yet be regarded as an open question’. In the words of Robert Olby, a historian and philosopher of science, ‘Through Muller’s widely read Pilgrim Lecture, this [sceptical] influence was spread to a wide audience.’
In a new series of extractions, with stringent quality checking, Avery attempted to confound his critics. McCarty left the laboratory in 1946, which was left in the hands of, amongst others, the meticulous Rollin Hotchkiss. Hotchkiss added several new chemical explorations of the extract, all further confirming that it was DNA. He disproved Mirsky’s objection by purifying the extract to the extent that the protein content was below 0.02 per cent and he showed that it was inactivated by a newly discovered crystalline enzyme specific to DNA: DNase. While many geneticists remained obdurate in their opposition, some were beginning to take notice.
In a subsequent interview with the biophysicist and future Nobel Laureate, the German-born physicist Max Delbrück, Horace F. Judson would discover that some distinguished researchers were aware of the potential importance of Avery’s discovery. ‘Certainly there was scepticism,’ Delbrück recalled. ‘Everybody who looked at it was confronted by this paradox. It was believed that DNA was a stupid substance … which couldn’t do anything specific. So one of these premises had to be wrong. Either DNA was not a stupid molecule, or the thing that did the transformation was not DNA.’ Avery had raised a monumentally important question and the only way of resolving the dilemma was for other researchers to probe it through some form of alternative experimentation to find out if he was right or wrong.
In 1951, two American microbiologists, Alfred Hershey and Martha Chase, undertook such an alternative experiment while studying the way that certain viruses use bacteria as a factory to make daughter viruses. These viruses are called ‘bacteriophages’, or ‘phages’ for short – from the Greek phago, which means to eat, because they devour cultures of host bacteria. The presence, and number, of viruses could be measured if you seeded your host bacteria into heat-softened agar and then added the viruses in various dilutions to the agar before spreading it over a laboratory plate. When the agar cooled it formed a thin, even layer of jelly in the plate, which, on overnight culture, would become clouded by growth of bacteria within the agar. Wherever a virus landed among the bacteria there would be a round window of transparency caused by the dissolving (lysis) of the bacteria which was easily visible, and thus countable. This ‘plaque-counting technique’, which I myself learnt from my microbiology professor as a medical student and later made use of in experiments on the nature of autoimmunity as a hospital doctor, is easily learnt and thus put to use by thousands of scientists in a great variety of experiments.
What interested Hershey and Chase was the fact that phage viruses were known to compose a core of genetic material surrounded by a capsule of protein. In fact, each virus closely resembled a medical syringe in structure, so that when it infected the bacterial cell of its host, it appeared to squeeze out the genetic material from the body of the syringe, leaving the empty protein coat attached to the outer bacterial cell wall. Meanwhile, the genetic material was injected into the bacterial cell interior, where the viral genome would be replicated as part of its reproduction. Hershey and Chase invented an ingenious experiment that would decide whether protein or DNA was the basis of the viral reproductive system. This would involve adding radioactive phosphorus and radioactive sulphur to the media in which separate batches of the host bacteria were growing. After four hours, to allow the radioactive element to be taken up by the bacteria, they introduced the phage viruses.
To understand the basis of the experiment we need to grasp that DNA contains phosphorus as part of its make-up but no sulphur, meanwhile the amino acids that make up proteins contain sulphur but no phosphorus.
By inoculating each of these two groups of bacteria with viruses, Hershey and Chase derived two populations of phage viruses – one containing the radioactive phosphorus and the other containing the radioactive sulphur. When the viruses infected the bacteria, they left their empty viral coats, mostly made up of protein, attached to the outside of the bacterial cell walls, having injected their core material, known to comprise DNA, into the bacterial bodies. Hershey and Chase used centrifugation to separate and extract empty viral coats. Meanwhile, the infected bacteria were allowed to go through their normal reproductive cycle, which allowed the viral cores inside them to generate entire new phage viruses, rupturing the bacterial bodies and flooding the growth media with large numbers of fully formed viruses. Hershey and Chase now removed what was left of the host bacterial bodies to gather dense concentrations of fully formed viruses.
When they now compared the empty viral coats, made up of protein, with the fully formed viruses, with their cores full of genetic material, they found that 90 per cent of the radioactive sulphur was left behind in the viral coats when the virus infected the cell, and 85 per cent of the phosphorus was now part of DNA that had entered the bacterial cell to code for the future offspring of virus. This confirmed Avery’s findings: DNA, and not protein, was the code of heredity.
We might duly note that this separation of coat from core DNA of virus involves a much higher degree of protein impurity than Avery’s extractions. Yet the hitherto sceptical geneticists appeared to be more convinced by the phage experiment than by Avery’s work. Perhaps the strikingly visual nature of the experiment was a factor. Perhaps it was the additional, quite different, avenue of confirmation. It didn’t harm credibility that leading geneticists were within the ‘phage camp’, too.
*
Today, with the advantage of retrospect, scientists by and large see the 1944 paper by Avery, MacLeod and McCarty as the pioneering discovery of DNA as the molecule of heredity. It has been portrayed as one of the most regrettable examples of a discovery that merited, but was not awarded, the Nobel Prize. There is ample evidence that Avery was recommended by senior colleagues, particularly within his own discipline of microbiology and immunology – indeed he was nominated twice, first in the late 1930s, for his work on the pneumococcal typing and its relevance to bacterial classification, and, after the 1944 paper was published, he was nominated yet again for his fundamental contribution to biology. But it would appear that the Nobel Committee was not sufficiently swayed. In retrospect, it is seen as a major omission that causes people to scratch their heads and wonder why.
Dubos worked for fifteen years in the lab next door to Avery’s and, in so much as the reticent Professor allowed it, he had plenty of opportunity to get to know Avery and to understand his approach to science and his reaction to the stresses involved in pioneering new concepts. In Dubos’ opinion, writing in 1976, the curious lack of recognition most likely derived from a combination of happenstance and Avery’s own personality. He would subsequently remark how, in all that time, Avery never closed the door of his lab, or the small office that led off it, allowing any of his staff to come and talk to him. This same eternally open door also allowed Dubos to witness ‘Fess’s’ activities at the bench, to listen in to his conversations with colleagues and to observe his interludes of introspective brooding.
This reserved, small and slender bachelor would inevitably arrive at work dressed in a neat and subdued style, his conservative attire somehow at one with the charm of his lively and affable behaviour. His eyes, under the domed bald head that seemed too voluminous for the frail body, were sparkling and always questioning, and he would transform the most ordinary conversation into an artistic performance with spirited gestures, mimicry, pithy remarks and verbal pyrotechnics. Avery might have been somewhat reticent in manner (he could be silently introspective), but in his own quintessential way he was vulnerably human, and that made him all the more interesting and enchanting.
I would suggest that creativity in science is every bit as intertwined with personality as one finds in a writer, artist, or musically gifted composer or performer. It would seem unsurprising in an artist if he appeared unusually ascetic, withdrawn from the hurly-burly world of the surrounding New York, ensuring that he lived close enough to the Rockefeller Institute so he could walk to work. In his ways, Avery could seem curiously ambivalent. He suffered mood swings at times, when alone in the lab, when he would appear to be dejected by the difficulties facing him. Afterwards he would declaim, clearly referring to himself, that resentment hurts the person who resents much more than the person who is resented. He left many letters unanswered and refused to have a secretary. He refused to review, or sponsor, any scientific paper in which he had made no contribution. In Dubos’ words, ‘Graciousness and toughness when it came to what he himself was determined to do, was part of his nature.’ Avery was a very successful teacher during his early medical career, yet in his later years he appears to have resented being expected to lecture on his own research. In this respect, he bore some interesting similarities to Charles Darwin. Avery scrupulously avoided any discussion of his own health and any intrusion, however small, into his private life – which was devoted to his younger brother, Roy, and to an orphaned first cousin whom he supported all through his life. He never expressed resentment about criticisms of his work, even when these were unjustified. He left no record of his private thoughts, other than the letters to his brother. A single experience struck Dubos as being significant.
One day, in early 1934, the same year that Avery suffered the onset of his thyrotoxicosis, Dubos told Avery that he was about to be married. The lady in question was a Frenchwoman living in New York, named Marie Louise Bonnet. Avery immediately rejoiced at the news. They were conversing in the laboratory on the sixth floor of the Rockefeller hospital building. During the subsequent animated conversation, Avery climbed out of his chair, walked to the window and looked out, as if lost for a moment in deep reflection. Returning to his chair, he mentioned that he had contemplated marriage years before, but that circumstances had not proved favourable to his plans. It seems likely that the lady in question was a nurse that Avery had met during the course he had taught to student nurses at the Hoagland Laboratory. Avery would have been about 32 years old at the time. For a moment or two the older man’s eyes were full of longing.
‘One of the great joys of life,’ he remarked to Dubos, ‘is to go home to someone who would rather see you than anybody else.’
Fate would prove cruel to both men. Marie Louise Bonnet subsequently died from tuberculosis at a time when Dubos was pioneering the very antibiotics that would eventually help to cure the same illness. The marriage was childless and the effects of his wife’s death on Dubos were devastating. He resigned, forthwith, from his antibiotic researches, which were later taken up by his former teacher, Selman Waksman at Rutgers Agricultural College, now Rutgers University, and which led to the discovery of a series of important antibiotics, including streptomycin. This breakthrough resulted in Waksman being awarded the Nobel Prize in Medicine or Physiology in 1952.
Much of what Dubos witnessed of Avery spoke of an intense focus and purity of purpose in science and his work. But, increasingly, his devotion to his research appeared to be accompanied by insularity bordering on reclusiveness.
Scientists who have laboured long and hard at a difficult but eventually rewarding line of research are usually happy to talk about it – if not to the media or ordinary social channels, certainly to colleagues. They travel to scientific symposia. They take part in conferences. They enjoy the camaraderie that comes from sharing the same interests. In the words of Frank Portugal, ‘wide-ranging discussions with peers both individually and at meetings are part and parcel of the scientific process. It is an important component of how collaborations are formed and scientific advances are made and respected.’ Most scientists are only too glad to accept the, often rare, honours and distinction their work brings their way. Not so Oswald Avery.
In 1944 Avery was proposed for an honorary degree at Cambridge University, a recognition most scientists would cherish. The following year he was awarded the Copley Medal by the Royal Society of London. Avery’s roots were English – in the late nineteenth century his family had emigrated to Canada from the city of Norwich – but he refused to visit England even on such prestigious occasions, putting forward the excuse that his state of health did not permit it except by travelling first class. In Dubos’ opinion, this was disingenuous, since the respective foundations would have funded the flights. That he might have felt nervous, claustrophobic, on the lengthy flight is possible. Recalling those dark moods in which Avery might mumble to himself about the damaging inflictions of resentment, it seemed more than likely to Dubos that he might have been unable to suppress lingering anger at the hurtful controversy provoked years ago by his polysaccharide typing of pneumococci. Whatever his reasons, Avery refused both honours.
An incident highlighted just how strong was Avery’s aversion to such formal acknowledgement of his work. Sir Henry Dale, who was President of the Royal Society in England, took it upon himself to bring the Copley Medal to the Rockefeller Institute, there to confer it on the shy and retiring Avery in person. Dale was accompanied by a Dr Todd, who knew Avery personally. The two highly respected English visitors arrived at the Institute in New York unannounced and went directly to Avery’s department in the main hospital building. But when they saw Avery working in his lab, through the ever-open door, they retreated without intruding on his presence.
Dr Todd would later recount how Sir Henry Dale said simply: ‘Now I understand everything.’
Bizarre as this behaviour would appear, it was in keeping with Avery’s increasingly reclusive personality: a man who avoided any of the normal personal contacts outside of immediate family and work colleagues. Genius can be strange. Yet such idiosyncratic behaviour apart, it was this son of an evangelical Baptist preacher who first discovered that DNA was the molecule of heredity. And putting such personal matters aside, the question remains: why was such a fundamental discovery not recognised by the awarding of the Nobel Prize?
In his letters to his brother, Avery retained a modest outlook. Could it be that a combination of Avery’s innate conservatism, his tendency to over-caution, and his downplaying of the implications of his discovery in the paper of 1944 might have contributed to his being overlooked? In Dubos’ words, the paper … ‘did not make it obvious that the findings opened the door to a new era of biology’. Dubos wondered if the Nobel Committee, unaccustomed to such restraint and self-criticism ‘bordering on the neurotic’ might have caused them to wait a while for both confirmation of the discovery and to see what the broader implications might be. To put it another way, Dubos questioned if the paper might have been a failure not in its own merits, as a scientific communication, but from the public relations point of view.
This lack of recognition is made all the more puzzling by the fact that, if the importance of the 1944 paper was not universally recognised when it was published, it became more and more obvious with the passage of time. The Hershey and Chase paper was published in 1952. And although he was retired by the time Crick and Watson published their famous discovery of the three-dimensional chemical structure of DNA in 1953, Avery was still alive. He wouldn’t die until two years later, in 1955.
More recently the Nobel authorities have allowed open access to their earlier thinking, and this has confirmed much of what Dubos had concluded. As part of the system for deciding who should get Nobel Prizes, the Nobel Committee receives proposals from leading experts around the world. In the words of Portugal, who reviewed their working and archives, ‘It seems that key biological chemists were not convinced by Avery’s claim that DNA was the basis of heredity.’ Not a single geneticist nominated Avery for the Nobel Prize. In part this may have reflected a difficulty in extrapolating his discovery in a single type of bacterium to genetics more widely, but even those colleagues who did nominate him for the Nobel Prize tended to overlook his work on DNA in favour of his immunological typing of the pneumococcal capsule. Portugal also wondered if Avery’s own idiosyncratic behaviour, including his reluctance to meet with and exchange findings with colleagues, and in particular geneticists, at scientific meetings had unintentionally confounded the acceptance of his groundbreaking discovery.
We are left with a lingering sense of regret that Avery was not accorded the recognition he deserved. He was 67 years old when his iconoclastic paper was published. It was, in the words of the eminent biochemist Erwin Chargaff, the rare instance of an old man making a major scientific discovery. ‘He was a quiet man: and it would have honoured the world more, had it honoured him more.’
But there is a greater acknowledgement of discovery than the awarding of a prize, no matter how respected and prestigious. In the words of Freeland Judson, ‘Avery opened up a new space in biologists’ minds.’ By space he meant he had unravelled a major truth, revealing new unknowns and raising important new questions. Avery himself had, with quintessential modesty, touched upon those important new questions in his letter to his brother:
If we are right, and of course that is not yet proven, then it means that nucleic acids are not merely structurally important but functionally active substances in determining the biochemical activities and specific characteristics of cells – and that by means of a known chemical substance it is possible to induce predictable and hereditary changes in cells. This is something that has long been the dream of geneticists … Sounds like a virus – may be a gene. But with mechanisms I am not now concerned – one step at a time – and the first is, what is the chemical nature of the transforming principle? Someone else can work out the rest …
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The Story in the Picture (#ulink_1f573ad9-98b3-558a-8d1f-470d1b6d5745)
You look at science (or at least talk of it) as some sort of demoralising invention of man, something apart from real life, and which must be cautiously guarded and kept separate from everyday existence. But science and everyday life cannot and should not be separated.
ROSALIND FRANKLIN
The discovery of the ‘transforming substance’ by Avery, MacLeod and McCarty, confirmed by Hershey and Chase’s elegant experiment with the bacteriophage, proved that DNA was the molecule of heredity. But both groups were working with microbes, bacteria and viruses, which were known to be much simpler in their hereditary nature than, say, animals and plants. This left huge unknowns that needed to be explored. Was DNA the key to the heredity of all of life, or was it just relevant to bacteria and viruses? By the early 1950s, work in many different laboratories had confirmed that DNA was a major ingredient in the nuclei of animals and plants. This supported the idea that DNA was the coding molecule of life. But if so, how did it really work? How, for example, did a single chemical molecule code for the complex heredity of a living organism?
Biologists, doctors, molecular biochemists and geneticists were now asking themselves the same, or similar, questions. Critical to any such understanding was the precise molecular structure of DNA. If, for example, we were to regard the role of DNA as akin to a stored genetic memory, how did that molecular structure enable the quality of such a phenomenally complex memory? How was that genetic memory transferred from parents to offspring? How did the same stored memory explain embryological development, where a single cell arising from the genomic union of a paternal sperm and maternal ovum gives rise to the developing human embryo and future adult human being?
There was another profoundly important question.
Darwinian evolution lay at the heart of biology. To put it simply, Darwin’s idea of natural selection implied that nature selected from a range of variations in the heredity of different individuals within a species. The way in which it worked was exceedingly simple, if brutal. Those individuals, and by inference their variant heredities, who carried a small advantage for survival and thus a better chance of giving rise to offspring, would therefore be more likely to contribute to the species gene pool. In reality natural selection worked more through a process of attrition. Those less advantaged individuals who did not carry the advantage for survival, were more likely to perish in the struggle for existence, and thus they were less likely to contribute to the species gene pool.
This is what Darwinian evolutionary biologists refer to as ‘relative fitness’. It is the measure of the individual’s contribution to the species gene pool. Certainly it has nothing to do with racist notions of superiority and inferiority attached to ‘survival of the fittest’ – a term introduced not by Darwin but by the social philosopher Herbert Spencer. But if we take a pause and think about it, such variant heredity, essential for natural selection to work, must also come about through mechanisms involving this wonder molecule, DNA, which must lie not only at the heart of heredity but also at the absolute dead centre of evolution. All of these questions needed to be answered by the scientists now struggling to understand the structure and, assuming structure was function, the properties of this remarkable chemical, DNA.
In fact the first step towards answering these questions had already been taken back in 1943, in what might appear unlikely circumstances. It was taken not by a biochemist, biologist or geneticist, but by an Austrian physicist. The spark was lit when, at 4.30pm on Friday 5 February, Erwin Schrödinger stepped up to the podium in Dublin to deliver a lecture that is now seen as a landmark moment in the history of biology. Schrödinger had been awarded the Nobel Prize in 1933 for work in quantum physics that expanded our understanding of wave mechanics – but I won’t confuse myself or my readers by entering further into the physics. The simple facts were that Schrödinger had exiled himself from his native Austria in protest at human rights abuses and had been given sanctuary in neutral Ireland by its President, Eamon de Valera. In Dublin Schrödinger had helped found the Institute for Advanced Studies. As part of his duties in support of the Institute, he had agreed to give a series of three lectures in which he developed a central theme: ‘What Is Life?’
Such was Schrödinger’s fame that the lecture theatre, which had a seating capacity for 400, could not accommodate all who wished to attend the lectures – this despite the fact that they had been warned in advance that the subject matter was a difficult one and that the lecture was not going to be pitched at an easy or popular level, even though Schrödinger had promised to eschew mathematics. De Valera himself was present in the audience, as were his cabinet ministers and a reporter for Time magazine. One wonders what these politicians and journalists made of Schrödinger’s focus on ‘how the events in space and time which take place within the spatial boundary of a living organism can be accounted for by physics and chemistry’.
Schrödinger subsequently extrapolated the three lectures into a book of less than a hundred pages with the same title: What Is Life? This was published the following year. In what is now a very famous book, Schrödinger popularised a quantum mechanics interpretation of the gene that had been proposed earlier by another distinguished physicist, the previously mentioned Max Delbrück.
In the opening pages of the first chapter, Schrödinger posed the question: ‘How can the events which take place within a living organism be accounted for by physics and chemistry?’ Admitting that at the time of writing the prevailing knowledge within the disciplines of physics and chemistry was inadequate to explain this, he nevertheless hazarded the opinion that ‘the most essential part of a living cell – the chromosome fibre – may suitably be called an aperiodic crystal’. The italicisation is Schrödinger’s to emphasise, as he further explained, that the physics up to this time had only concerned itself with periodic crystals, the kind of repetitive atomic structures seen, for example, in very obvious crystalline compounds such as gemstones.
What did he mean by an ‘aperiodic crystal’?
He explained this with a metaphor. If we examined the images within the pattern of a wallpaper, we could see how the pattern was repeated, over and over. This was the equivalent of a periodic crystal. But if we examined the complex elaboration of a Raphael tapestry, we saw a pattern of images that did not repeat themselves, yet the pattern was coherent and meaningful.
Schrödinger intuited further.
It was the chromosomes, or more likely an axial fibre much finer than what was visible under the microscope, that contained what he termed ‘some kind of code-script’ that determined the blueprint of the individual’s development from fertilised egg to birth – and further determined the functioning of what we would now term the genome throughout the lifetime of the individual.
That intuition would provide the drive for a naïve but highly inquisitive young American, called James Dewey Watson, to join forces with a slightly older but equally inquisitive Englishman, Francis Crick, and form what is now seen as one of the most famous partnerships in scientific history. Both men would take their inspiration from Schrödinger to search for the aperiodic crystal that coded for DNA.
*
Watson was an exceptionally bright child who lived at home with his family in Chicago while attending the local university. He enrolled when aged just 15 and he graduated, aged 19, in 1947 with a bachelor’s degree that included a year studying zoology. His teacher of embryology would remember him as a student who showed little interest in lectures and made no notes whatsoever, so it was all the more puzzling when he graduated top of his class. Watson would subsequently admit to a habitual laziness. Though vaguely interested in birds, he had deliberately avoided any courses that involved chemistry or physics of ‘even medium difficulty’. This self-indulgent student left Chicago with only a rudimentary knowledge of genetics or biochemistry. As part of his education he had attended lectures by the geneticist Sewall Wright, who had devised a mathematical system of studying population genetics. Wright’s course included a discussion of Avery’s work, but Watson would subsequently confess that he took little notice. He would also confess that the inspiration for his subsequent interest in the ‘mystery of the gene’ was Schrödinger’s book, What Is Life?
Inspired by this book, Watson landed a research fellowship at Indiana University, at Bloomington. He was delighted by the move because Nobel Laureate Hermann Joseph Muller was the local Professor of Zoology. As early as 1921 Muller had observed that the genes of the fruit fly underwent mutations – as did the genes of the bacteriophages – the viruses that had inspired Hershey and Chase. Watson was intrigued by the fact that phage viruses could be manipulated in test tubes. Their reproductive cycles were extremely brief – an important consideration for an impatient young scientist. There were simple test systems that could be employed to follow their life cycles, and numbers, in a way that would open up new angles from which to attack the gene problem. All you had to do was carefully design an experiment aimed at probing some particular aspect of the gene problem and the whole shebang could be completed in a matter of days. This intimate, if brutal, interplay between phage viruses and their host bacteria allowed scientists to figure the complex chemistry of genes, genetics and chromosomes.
Curiously it would not be Muller but another phage researcher, Salvador Luria, who would now give shape and direction to the young scientist’s growing infatuation with the gene.
The Italian-born Luria was another European scientist – a microbiologist, like Avery – who found refuge in America from the European war zone. By now he had entered into a working collaboration with Max Delbrück, who was Professor of Biology at the California Institute of Technology. In 1943 Luria and Delbrück designed and conducted an experiment that demonstrated that genetic inheritance in bacteria followed precise evolutionary principles. This experiment became one of the foundation stones of modern Darwinism. That same year Delbrück befriended another microbiologist called Alfred Hershey, who would subsequently write the key DNA paper with Martha Chase. In a letter to Luria, Delbrück summarised Hershey as follows: ‘Drinks whiskey but not tea. Likes living in a sailboat … Likes independence.’ The three scientists joined forces to become the nucleus of a cooperating and mutually supportive network of scientists that would become known as the ‘phage group’. Delbrück would subsequently explain that they would be a group only in the sense that they communicated freely on a regular basis, and that they told one another what they were thinking and doing. In this way a loose creative movement grew around the two European expatriate scientists, all working towards the common ambition of figuring out how genes worked.
Luria, Delbrück and Hershey now posed some interesting questions. How does the phage virus actually get into the bacterium? How, once inside, does it multiply? Does it multiply like a bacterium, growing and budding off daughter viruses? Or does it multiply by an entirely different mechanism? Is this multiplication some complex physical or chemical process that could be understood in terms of known physical and chemical principles? Through making use of the phage reproductive system, they hoped to solve the mystery of the gene. To begin with it all seemed simple in principle, but as experiment followed experiment and year followed year, they found themselves no closer to the answer.
Up to 1940 or so, people like Delbrück and Luria had assumed that viruses were simple. They had little to go on since the majority of viruses were so minuscule they could not be seen with any clarity through the ordinary light microscope. They would even talk about them as if they were akin to protein molecules. Luria would come to define phage viruses, in a misleading oversimplification, as extensions of the bacterial genome. But with the invention of the electron microscope, by the German company Siemens, even the smallest viruses, including bacteriophages, would soon become visible for the first time. And when they did become visible, they proved to be more complex than the two scientists had initially conceived.
Many phages had a head that was cylindrical in shape, with a narrow sheath below it, as tall as the head, and a base plate with six spikes with fibres attached. Now that they could visualise phages in the process of infecting their host bacteria, something struck Delbrück and Luria as exceedingly odd. The viruses didn’t actually pass through the bacterial cell wall. What they appeared to do was to squat down against the wall and inject their hereditary material into the cell. In 1951 a phage researcher called Roger Herriott would write to Hershey, ‘I’ve been thinking that the virus may behave like a little hypodermic needle full of transforming principles.’ This became the background to Hershey and Chase’s experiment in which they confirmed that that was precisely what happened. The virus behaved exactly like a hypodermic syringe; the tail and its elongated fibrils would attach to the bacterial wall and the phage would then inject its viral DNA in through the bacterial wall to take over the bacterium’s own genetic machinery, the viral genome compelling the bacterial genome to construct what was necessary for the generation of daughter viruses. In effect, the infected bacterium became a factory for the production of daughter viruses.
It would be this discovery, together with many associated extrapolations to microbiology and genetics, that would lead to all three scientists – Delbrück, Luria and Hershey – sharing the Nobel Prize in 1969.
Meanwhile, back in 1947, it was the dynamic energy and infectious charm of Luria, and the innovative genius of Delbrück, that proved most influential to the youthful Watson after his arrival into Indiana University. Still fascinated by the mystery of the gene, it was his hope that the mystery might be solved without his bothering to learn any of the complex physics or chemistry.
It is instructive to discover, from conversations between Luria and Watson, that there was no ignorance at Bloomington about Avery’s discovery of DNA. Luria had visited Avery in 1943, prior to the publication of the key paper, when he had the opportunity of discussing Avery’s findings in detail. He would recall Avery to Watson as an utterly non-pompous scientist, precise in his language, with a tendency as he spoke to close his eyes and rub his bald head – ‘every bit of a chemist, even though he was an MD’. Watson would take his cue from Luria, writing, in The Double Helix, how Avery had shown that hereditary traits could be transmitted from one bacterial cell to another by purified DNA molecules. Given the fact that DNA was known to occur in the chromosomes of every type of living cell, ‘Avery’s experiments strongly suggested that … all genes were composed of DNA.’
In the autumn of 1947, Watson, still just 19, took Luria’s course in bacteriology and Muller’s in X-ray-induced gene mutation. Faced with the choice of entering into research with Muller on Drosophila or with Luria on microbes, he plumped for Luria, despite the fact that the Italian scientist had a reputation among the graduate students for having a short fuse with dimwits. Watson would subsequently adopt his patron’s example. Delbrück was a heroic figure to Watson because he had inspired Schrödinger’s ideas in the inspirational book. Watson was delighted when Luria introduced him to Delbrück when the eminent German physicist paid a visit to Bloomington.
Luria set Watson a PhD dissertation on the pathological effects on phage of exposure to X-rays. The work proved so mundane that Watson would barely mention it in his biography. But his obsession with the gene was undimmed. By the summer of 1949, his thesis nearing completion, he had the itch to travel to Europe. Luria arranged a Merck Fellowship from the National Research Council – three thousand dollars for the first year, potentially renewable. In May the following year, with his PhD under his belt, he sailed for Denmark, where he had been assigned to study nucleotides with a biochemist named Herman Kalckar. Kalckar was a gifted scientist but his interest was neither the gene nor the bacteriophage. A disenchanted Watson switched his attentions to another Dane, and a member of the phage group, Ole Maaløe, who was working on the transfer of radioactively-tagged DNA from phages to their viral offspring.
Out of the blue, Kalckar accepted a short-term project in the Zoological Station in Naples. He suggested that Watson might tag along. Though he had little interest in marine biology, Watson was delighted to acquiesce. He hoped to warm himself in the Italian sun. But he was disappointed to find Naples chilly, with no heater in his room on the sixth floor of a nineteenth-century house. ‘Most of my time I spent walking the streets or reading journal articles … I daydreamed about discovering the secret of the gene, but not once did I have the faintest trace of a respectable idea.’
Here, by happenstance, he attended a lecture in the Zoological Station given by an English scientist named Maurice Wilkins. The lecture could hardly have excited him in prospect, knowing that most of it would be about the biochemistry of proteins. ‘Why should I get excited learning boring chemical facts as long as the chemists never provided anything incisive about the nucleic acids?’
But he took the risk and attended anyway.
Tall, bespectacled, asthenic and somewhat diffident in manner, you might have expected Wilkins’ presentation to bore the restless and impatient Watson. But it did not. To begin with, it was delivered in a language that Watson readily understood. And for all of his diffident manner, Wilkins kept to the point. Then suddenly, close to the end of the lecture, a projected slide jarred Watson to full attention. On the screen was a photograph that showed something Wilkins called an X-ray diffraction pattern of DNA that had been taken in the King’s College laboratory in London. Watson would subsequently admit that he knew nothing about X-ray crystallography. He hadn’t understood a word of what he had read about it in the scientific journals and he thought that much of what the ‘wild crystallographers’ were claiming was very likely baloney.
But now here was Wilkins mentioning in passing that this was the clearest picture of DNA that he and his colleagues had yet obtained from their X-ray studies. In the same audience was the Leeds-based English physicist, William Astbury, who had pioneered X-ray diffraction studies of biological molecules, and who had produced the first X-ray pictures of DNA. Astbury would subsequently confirm that no one had ever shown such a sharp, discrete set of reflections from the DNA molecule as Wilkins then projected onto the screen. ‘There was nothing like it in the literature.’ In explaining the picture, Wilkins suggested that DNA might be thought of as a crystalline substance.
Watson was electrified to hear Schrödinger’s prophecy confirmed. He sat in a daze of wonderment as Wilkins went on to explain that if and when we understood the structure of DNA, then we might be in a better position to understand how genes worked. Watson was now asking himself some pertinent questions. Who was this interesting English scientist, Wilkins? And how could he get to join his team at King’s College in London?
*
Maurice Hugh Frederick Wilkins was not, in fact, English, as Watson initially surmised. He was born in Pongaroa, New Zealand, where his father, Edgar Henry, was a practising doctor. The family were Anglo-Irish in origins, hailing from Dublin, where Maurice’s paternal grandfather had been headmaster of the high school and his maternal grandfather chief of police. On leaving New Zealand the family first returned to Ireland, then headed for London, where Dr Wilkins was later to do his pioneering work in public health.
Maurice had had a natural scientific curiosity even as a boy, and it was this curiosity that led to his studying physics as part of his BA at Cambridge University, after which he worked for his PhD under John Turton Randall (later knighted), a physicist who played a leading role in the development of radar during the war.
As a postgraduate, Wilkins moved to the University of Birmingham, following the posting of his Cambridge tutor, Randall, where the two scientists continued their collaboration on radar. But then, out of the blue, Wilkins found himself dispatched to the United States to work on the Manhattan Project. His purpose was to figure out how to purify suitable isotopes of uranium from impure sources, to make them suitable for the atomic bomb. In February 1944 Wilkins crossed the dangerous waters of the Atlantic on the Queen Elizabeth, heading for the University of Berkeley, California. Here he made a modest contribution to the development of the atomic bomb. However, the subsequent destruction of Hiroshima and Nagasaki by the very weapons that he had worked on left Wilkins somewhat unsettled in conscience.
After the war Wilkins returned to England, where he ended up as assistant director of the new Biophysics Unit at King’s College London, funded by the Medical Research Council, and where his former boss, Randall, was now the Wheatstone Professor of Physics. The new departmental remit was to apply the experimental methods of physics to important biological problems. This would result in Wilkins developing a relationship with Watson and Crick and joining the search for the molecular code of DNA. It would also involve him in a somewhat infamous strained working relationship with the X-ray crystallographer Rosalind Franklin.
Given this developing history, we might pause a moment or two to consider Wilkins’ personality, and its relevance to the com-ing storm. From what one can gather from his belatedly published biography, and the memory of those who knew him and worked with him, Wilkins was a quiet, highly moral man, somewhat Quaker-like in social attitudes. As a boy he enjoyed a close emotional relationship with his elder sister, Eithne, who taught him to dance. But this intimacy was torn apart when Eithne developed a bacterial infection that turned into a septicaemia, the blood-borne infection provoking septic arthritis in multiple joints. This would have been a shockingly painful and disabling condition, which, prior to antibiotics, might have proved fatal. She spent months in a hospital bed, with her limbs dangling from hoists, her joints lanced open to drain the pus. The unfortunate Eithne survived but the intimacy with her younger brother ended. The trauma of this experience may well have affected his self-confidence, particularly in his relationships with women.
While an undergraduate at Cambridge, he fell in love with a woman called Margaret Ramsey, but he ‘was incapable of making a suitable advance to her’. After he told her of his love, there was a short silence after which she walked from the room. During his stay in Berkeley, Wilkins was attracted to an artist named Ruth, who had shared lodgings with him. She conceived a child and they subsequently married, but when, as the war was ending, he informed Ruth that he intended to return to the UK, she refused to accompany him. ‘Ruth told me one day that she had made an appointment for me with a lawyer and when I arrived at his office I was shocked to hear that Ruth wanted to end our marriage.’ Shortly after the divorce, Ruth gave birth to a son. Wilkins went to see her, and their baby, in the hospital ward, before returning to the UK alone.
Wilkins would admit to difficulty overcoming an innate shyness, and he would require periodic psychotherapy in his time working at King’s, but he subsequently found a wife, Patricia, who appreciated the sensitive soul behind the diffident exterior, and he enjoyed a happy marriage and the joys of rearing a family of four children. There was also a fruitful outcome of his unsettled conscience following his work on the Manhattan Project. Before leaving Berkeley, one of his working colleagues came to his rescue … ‘Seeing I wanted to find some new direction, he lent me a new book with the rather ambitious title, What Is Life?’
four (#ulink_2a07bc6a-42b5-5437-9335-fbe67e5a89a5)
A Couple of Misfits (#ulink_2a07bc6a-42b5-5437-9335-fbe67e5a89a5)
Francis likes to talk … He doesn’t stop unless he gets tired or he thinks the idea’s no good. And since we hoped to solve the structure by talking our way through it, Francis was the ideal person to do it.
JAMES WATSON
It is somewhat ironic that Maurice Wilkins only arrived in Naples by happenstance, since he was substituting for Randall, who had agreed to present the talk but had been unable to attend. It seems unlikely, had Randall himself presented the lecture, that he would have included the DNA slide, or that he would have spoken of what it portrayed with such clear reference to Schrödinger’s book. This lecture, which so excited Watson, was on the physico-chemical structure of big biological molecules, mostly proteins, made up of thousands of atoms. The key photograph had been taken by Wilkins, working together with a graduate student called Raymond Gosling while using a technique called X-ray diffraction.
One of the things this technique was particularly good at was finding the sort of repetitive molecular themes you found in crystals, hence the other term for it: X-ray crystallography.
‘Suddenly,’ as Watson would later recall, ‘I was excited about chemistry.’
Up to this moment Watson had had no idea that genes could crystallise. To crystallise, substances must have a regular atomic structure – a lattice-like structure of atoms at the ultramicroscopic level. The youthful Watson appears to have been a wonderfully free spirit journeying from one interesting encounter to another. Impulsive, impatient, egregiously direct, yet all the while on the hunt for new adventure.
‘Immediately I began to wonder whether it would be possible for me to join Wilkins in working on DNA.’ But Watson never got to work with Wilkins. Instead, happenstance headed him in the direction of another X-ray crystallographer called Max Perutz, who was working at the Cavendish Laboratory at Cambridge University.
The Cavendish Laboratory is a world-famous department of physics. First established in the late nineteenth century to celebrate the work of British chemist and physicist Henry Cavendish, one of its founders and the first Cavendish Professor of Physics was James Clerk Maxwell, famous for his development of electromagnetic theory. The fifth Cavendish Professor and the director of the laboratory at the time of Watson’s arrival was William Lawrence Bragg, who was the successor, as director, to Lord Ernest Rutherford, another Nobel Prize-winner and the first physicist to split the atom. Bragg was an Australian-born physicist who, jointly with his father, had been awarded the Nobel Prize in Physics in 1915 for establishing the use of X-rays in analysing the physico-chemical structures of crystals. X-ray beams are bent when they pass through the orderly atomic lattice of crystals. What is projected onto the photographic plate is not the picture of the atoms within the structure but the refracted pathways of the X-rays after they have collided with the atoms. This is called ‘diffraction’ and is similar to how light is bent when it passes through water. In a structure with haphazard positioning of atoms in space, the X-rays will be scattered randomly and form no pattern. But in a structure that contains atoms in a repetitive atomic lattice – such as a crystal – the X-rays are deflected in a recognisable pattern of blobs on the X-ray plate. From this diffraction pattern, the atomic structure of the structure can be deduced.
The two Braggs – father and son working as a team at the University of Leeds – had constructed the first X-ray spectrometer, allowing scientists to study the atomic structure of crystals. At the age of 22, Bragg Junior, now a Fellow of Trinity at Cambridge, had produced a mathematical system, Bragg’s Law, that enabled physicists to calculate the positions of the atoms within a crystal from the X-ray diffraction pictures. At the time of Watson’s arrival into the laboratory, Bragg’s main focus of study was the structure of proteins. It was this potential for the X-ray diffraction of proteins that had attracted Max Perutz to the Cavendish Laboratory.
Born in Vienna of Jewish parentage, Perutz was another enforced exile who had settled in England and become a research student at the Cavendish Laboratory. He completed his PhD under Bragg and subsequently devoted most of his professional life to the analysis of the macromolecule of haemoglobin, the pigment that colours the red cells in our blood, enabling them to carry oxygen around the body. Also working at the Cavendish was an unusual young scientist, Francis Crick. The English-born scientist had graduated with a BSc in physics from University College London aged 21, but thanks to war duty and a profound antipathy to his PhD project (he was supposed to be working on the viscosity of water at high temperatures) he, like Watson, found an alternative source of inspiration in Schrödinger’s book. In Crick’s own words, ‘It suggested that biological problems could be thought about in physical terms.’
But what terms?
At the time Crick wasn’t as convinced by Avery’s discovery as Watson was. Like Schrödinger himself, Crick was more inclined to the protein hypothesis. But he was every bit as impressed with Schrödinger’s ‘code-script’ idea as Watson. What then could he possibly make of Schrödinger’s conception of an aperiodic crystal?
Simple crystals such as sodium chloride, the basis of common salt, would be incapable of storing the vast memory needed for genetic information because their ions are arranged in a repetitive or ‘periodic’ pattern. What Schrödinger was proposing was that the ‘blueprint’ of life would be found in a compound whose structure had something of the regularity of a crystal, but must also embody a long irregular sequence, a chemical structure that was capable of storing information in the form of a genetic code. Proteins had been the obvious candidate for the aperiodic crystal, with the varying amino acid sequence providing the code. But now that Avery’s iconoclastic discovery had been confirmed by Hershey and Chase, the spotlight fell on DNA as the molecular basis of the gene. Suddenly new vistas of understanding the very basics of biology, and medicine, appeared to be beckoning.
It was through a mixture of luck and the gut reaction of Perutz that the dilettantish Crick was taken into the fold of the Cavendish. In Perutz’s recollection, Crick arrived in 1949 with no reputation whatsoever in science. ‘He just came and we talked together and John Kendrew and I liked him.’ And so the likeable Crick ended up, in such an idiosyncratic process of selection, working on the physical aspects of biology – what today we call molecular biology – under the guidance of Bragg, Perutz and Kendrew, at the Cambridge laboratory.
In 1934, John Desmond Bernal, an Irish-born scientist with Jewish ancestry and a student of Bragg Senior, had shown for the first time that even complex organic chemical molecules, such as proteins, could be studied using X-ray diffraction methods. Bernal was a Cambridge graduate in mathematics and science, who was appointed as lecturer to Bragg at the Cavendish in 1927, becoming assistant director in 1934. Together with Dorothy Hodgkin, Bernal pioneered the use of X-ray crystallography in the study of organic chemicals – the chemicals involved in biological structures – including liquid water, vitamin B1, the tobacco mosaic virus and the digestive enzyme, pepsin. This was the first protein to be examined at the Cavendish in this way. When, in 1936, Max Perutz arrived as a student from Vienna, he extended Bernal’s work to the X-ray study of haemoglobin.
By the time Crick joined the laboratory, Sir William Bragg had been replaced by Sir Lawrence Bragg, and John Kendrew and Max Perutz had taken Bernal’s findings further to become bogged down in a ‘disastrous paper’ on the chain structures of proteins. And now we discover something distinctly unusual about Francis Crick, something that Perutz may have intuited at their meeting. He had an avid curiosity about science, reading very widely, and he was equipped with a mind capable of amassing a formidable knowledge base across different disciplines. One of the first things he did after his arrival into the Cavendish was to acquaint himself with everything his bosses had achieved. Junior as he was, Crick now took it upon himself to undertake a long, critical look at their work. This he then proceeded to criticise from basic principles. At the end of his first year in the department, Crick presented his criticisms in the form of an ad hoc seminar, borrowing his title from Keats as ‘What Mad Pursuit’. He began with a twenty-minute summary of the deficiencies in the departmental methods before pointing out what he saw as the ‘hopeless inadequacy’ of their investigation of the structure of the haemoglobin molecule. The X-ray analysis of haemoglobin was of course Perutz’s main objective. Bragg was infuriated by the cocky behaviour of this upstart junior colleague, but Perutz would subsequently admit that Crick was right and proteins were far more complicated in their structures than they had initially assumed. Restless and ever-inquisitive, Crick proved to be an uneasy, sometimes downright embarrassing import into the scientific pool of the laboratory. And while Bragg and Perutz saw proteins as the great unsolved puzzle, Crick was more interested in the mystery of the gene.
As 1949 elided into 1950, Crick would subsequently confess that he still did not realise that the genetic material was DNA. But he knew that genes had been plotted out in linear arrays along the chromosomes by people like Barbara McClintock, and that proteins, which had to be the expression of the genes, were also being plotted out as linear arrays, however lengthy and complicated. There had to be some logical way in which one translated into the other. By 1951, two years after his arrival into the Cavendish Laboratory, Crick perceived that these were two different, if necessarily related, puzzles – the mystery of how genes appeared able to copy themselves, and the mystery of how the linear structures of genes translated into the linear structures of proteins.
The wide-reading, voraciously inquisitive Crick needed what Judson termed a catalyst. This arrived in the form of the gangly, equally inquisitive Watson that same year, 1951. From their first meeting, it would appear that here was one of those rare working conjunctions of two odd-ball personalities that, when they come together, make an extraordinary creative whole that is more than the sum of the individual ingenuities. And yet it very nearly didn’t happen.
*
We should recall that Watson was extremely junior within the department. A recent PhD graduate, he had arrived into Kalckar’s laboratory on a Merck Fellowship funded by the US National Research Council. The terms and conditions were laid down and signed for back home, but now here he was abandoning those carefully laid intentions to gallivant from the work in Denmark to follow some giddy new inspiration in England, a place he had never visited in his life and where he knew absolutely nobody. Impulsive and single-minded, Watson would subsequently confess that his head was filled with curiosity about that single DNA photograph. He had tried to engage with Wilkins in Naples after the lecture, at a bus stop during an excursion to the Greek temples at Paestum. He had even tried to take advantage of a visit from his sister, Elizabeth, who had arrived to join him as a tourist from the States. Now here were Maurice Wilkins and Watson’s sister, Elizabeth, finding a common table to take lunch together. Watson sensed an opportunity and barged in, with the intention of ingratiating himself with Wilkins. But the self-effacing Wilkins excused himself, to allow brother and sister the privacy of the table.
His plans foiled, Watson refused to let go of this exciting new avenue of interest. ‘I proceeded to forget Maurice, but not his DNA photograph.’
He stopped over in Geneva for a few days to talk to a Swiss phage researcher, Jean Weigle, who provoked yet more excitement by informing Watson that the eminent American chemist, Linus Pauling, had partly solved the mystery of protein structure. Weigle had attended a lecture by Pauling, who like Bragg in Cambridge had been working with X-ray analysis of protein molecules. Pauling had just made the announcement that the protein model followed a uniquely beautiful three-dimensional form – he had called it an ‘alpha-helix’. By the time Watson arrived back in Copenhagen, Pauling had published his discovery in a scientific paper. Watson read it. Then he re-read it. He was confounded by his lack of understanding of X-ray crystallography. The terminology, in physics and chemistry, was so far beyond him that he could only grasp the most general impression of its content. His reaction was so childishly naïve as to be touching: in his head he devised the opening lines of his own imagined paper in which he would write about his discovery of DNA, if and whenever he discovered something of similar portent.
But what to do to get on board the DNA gravy train?
He needed to learn more about X-ray diffraction studies. Ruling out Caltech, where Pauling would react with disdain to some ‘mathematically deficient biologist’, and now ruling out London, where Wilkins would be equally uninterested, Watson wondered about Cambridge University, where he knew that somebody called Max Perutz was following the same X-ray lines of investigation of the blood protein molecule, haemoglobin.
‘I thus wrote to Luria about my newly found passion …’
The world of science was smaller in 1951 than it is today. Even so, it would appear a hopelessly optimistic ambition for this impulsive young graduate to merely ask his mentor to fix his arrival into a leading laboratory in England to engage in a line of research that he knew absolutely nothing about.
The amazing outcome was that Luria was able to do so. By happenstance, he met Perutz’s co-worker, John Kendrew, at a small meeting at Ann Arbor, in Michigan, where, by a second and equal happenstance, there was a meeting of minds – both scientific and social. And by a third happenstance, Kendrew was looking for a junior to help him study the structure of the muscle-based protein myoglobin, which contained iron at its core and held on to oxygen, just like the haemoglobin in the blood.
Twice in his short career the young American scientist had leapt into the unknown and landed on his feet. First it had been through Luria’s patronage in Bloomington, and by extension also Delbrück’s, two of the co-founders of the phage group; and now the gift of happenstance extended further, again through Luria’s patronage, to Kendrew, and by proxy to the Cambridge laboratory and Max Perutz. Watson’s arrival into the laboratory would bring him under the ultimate tutelage of Sir Lawrence Bragg, a founder of X-ray crystallography. It would connect him directly to his future partner in DNA research, Francis Crick, and further afield – through the connection between the Cambridge laboratory and the X-ray laboratory at King’s College London – with Maurice Wilkins and a young female scientist, Rosalind Franklin, who were working on the X-ray crystallography of DNA.
five (#ulink_191c9ae8-887d-5869-af27-b063095aa353)
The Secret of Life (#ulink_191c9ae8-887d-5869-af27-b063095aa353)
I think there was a general impression in the scientific community at that time that [Crick and Watson] were like butterflies flicking around with lots of brilliance but not much solidity. Obviously, in retrospect, this was a ghastly misjudgement.
MAURICE WILKINS
In the opening pages of his brief, witty and brutally candid autobiography, James Watson recounts a chance meeting in 1955 with a scientific colleague, Willy Seeds, at the bottom of a Swiss glacier. It was two years after the publication of the discovery of DNA. Watson and Seeds were acquainted, Seeds having worked with Maurice Wilkins in probing the optical properties of DNA fibres. Where Watson had anticipated the courtesy of a chat, Seeds merely remarked, ‘How’s Honest Jim?’, before striding away. The sarcasm must have bitten deep for Watson to not merely remember it distinctly, but even to consider the term ‘Honest Jim’ as the initial title of his life story, before being persuaded to adopt the more descriptive alternative, ‘The Double Helix’. It was as if the former colleague was questioning Watson’s right to be recognised as the co-discoverer of the secret of life.
He had been taken aback, reflecting on meetings with the same colleague in London a few years earlier, at a time when, in Watson’s words, ‘DNA was still a mystery, up for grabs … As one of the winners, I knew the tale was not simple, and certainly not as the newspapers reported.’ It was a more curious story, one in which his fellow-discoverer, Francis Crick, would freely admit that neither he nor Watson was even supposed to working on DNA at the time. Equally curious was the fact that up to the day of the discovery, neither Watson nor Crick had contributed anything much to the many different scientific threads and themes that, when finally put together, like the pieces of a remarkable three-dimensional jigsaw puzzle, laid the molecular nature of DNA bare for the first time in history.
Watson’s welcome into the Cambridge laboratory was quintessentially English in its lack of formality. He arrived in Perutz’s office straight from the railway station. Perutz put him at his ease about his prevailing ignorance of X-ray diffraction. Both Perutz and Kendrew had come to the science from graduation in chemistry. All Watson needed to do was to read a text or two to become acquainted with the basics. The following day Watson was introduced to the white-moustached Sir Lawrence, to be given formal permission to work under his direction. Watson then returned to Copenhagen to collect his few clothes and tell Herman Kalckar about his good luck. He also wrote to the Fellowship Office in Washington, informing them of his change of plans. Ten days after he had returned to Cambridge he received a bombshell in the post: he was instructed, by a new director, to forgo his plans. The Fellowship had decided he was unqualified to do crystallography work. He should transfer to a laboratory working on physiology of the cell in Stockholm. Watson appealed once more to Luria.
As far as Watson was concerned it was out of the question to follow these new instructions. If the worst came to the worst, he would survive for at least a year on the $1,000 still left to him from the previous year’s stipend. Kendrew helped him out when his landlady chucked him out of his digs. It was just another indignity when he ended up occupying a tiny room at Kendrew’s home, which was unbelievably damp and heated only by an aged electric heater. Though it looked like an open invitation to tuberculosis, living with friends was preferable to the sort of digs he might be able to afford in his impecunious state. And there was a comfort to be had:
‘I had discovered the fun of talking to Francis Crick.’
And talk they did.
In Crick’s own memory: ‘Jim and I hit it off immediately, partly because our interests were astonishingly similar and partly, I suspect, because a certain youthful arrogance, a ruthlessness, and an impatience with sloppy thinking came naturally to us both.’ That conversation, lasting for two or three hours just about every day for two years, would unravel the most important mystery ever in the history of biology – the molecular basis of heredity.
We need to grasp a few fundamentals to understand how this happened. Firstly, we have two young and ambitious men – in Watson’s case aged just 23, in Crick’s, aged 35 – who were both exceptionally intelligent and surrounded by the ambience of high scientific endeavour and achievement. We need to grasp that Watson’s interest, intense and obsessive, was the structure of DNA in its potential to explain the mystery of the workings of the gene, and thus the storing of heredity. We also need to grasp the slight, but important, difference with Crick’s interest, which was not DNA, or even the gene in itself, but the potential of DNA to explain how Schrödinger’s mysterious molecular codes – his aperiodic crystals – had the potential not only for coding heredity but for translating from one code to another, from the gene to the second aperiodic crystal that must determine the structure of proteins.
Crick would subsequently recall Watson’s arrival in early October 1951. Odile, his French second wife, and he were living in a tiny ramshackle apartment with a green door that they had inherited from the Perutzes. Conveniently situated for the centre of Cambridge and only a few minutes’ walk from the Cavendish Laboratory, it was all they could afford on Crick’s research stipend. The ‘Green Door’, as it was thereafter called, consisted of an attic over a tobacconist’s house, with ‘two and a half rooms’ and a small kitchen that was reached by climbing a steep staircase off the back of the tobacconist’s house. The two rooms served as living room and bedroom for Crick and Odile, with the half room providing a bedroom for Crick’s son, Michael – born to his first wife, Ruth Doreen – when Michael was home from boarding school. The wash-room and lavatory opened halfway up the stairs and the bath, covered with a hinged board, was a feature of the tiny kitchen.
One day, out of the blue, Perutz brought Watson to the flat. Crick was out. But he would recall Odile remarking that Max had come round with a young American who ‘had no hair’. The newly arrived Watson was sporting a crew-cut – a hairstyle uncommon in England at the time. They met within a day or two … ‘I remember the chats we had over those first two or three days in a broad sort of way.’
Both men were impecunious, but it hardly mattered since they were uninterested in money. What mattered was that the deeply personal, deeply intellectual, symbiosis had begun. Crick brought a rowdy enjoyment of problem solving, together with the hubris, born out of his background in physics, to believe that the big problem facing them – the mystery of the gene – was indeed solvable. Watson, who had little knowledge of physics or X-ray crystallography, brought a mine of knowledge about the way in which genes worked – the fruits of the bacteriophage researches of Luria and Delbrück. Perutz would subsequently confirm that the arrival of Watson, at that particular moment of time, was opportune for the workings of the Cavendish Lab, where his enthusiastic personality appeared to have galvanised Crick, and where his knowledge of the field of genetics added an exotic aspect to the structural physics and chemistry that otherwise prevailed. Moreover, different as their backgrounds were, Crick and Watson shared a deep, insatiable level of curiosity about the puzzle that lay at the very root of biology: they were determined, almost from their first meeting, that they would solve the mysterious nature of the gene.
The first creative step was to realise that the answer lay with DNA. To be more accurate, they realised that somehow chemical structure must parallel function: so the answer to the great conundrum lay in the three-dimensional chemical structure of DNA. But nobody really knew what shape or form this structure took. To the minds of Crick and Watson at that particular moment in time, it would have seemed nothing more than a ghost in the mist.
New discoveries in science will usually involve a lengthy period of laboratory labour, with knowledge growing by hard-won increments, often involving contributions from several, or a good deal more than several, different sources. In many ways the struggle to get to grips with the mysteries of heredity followed exactly such a course. But the mundane sweat of the laboratory aspects, the growth of knowledge by hard-won increments, would not fall to Watson and Crick. These would be left to others. The Crick–Watson symbiosis would be founded on a second, equally important ingredient of scientific advance, and one that has commonalities with the advances in the arts and humanities: this is the quintessentially human gift we call ‘creativity’.
Within the hierarchy of the lab, Crick and Watson were the lowest contributing level. In Crick’s words, ‘I was just a research student and Jim was just a visitor.’ They read very widely, imbibing the fruits of the hard work of others. They talked and talked, thinking out loud, probing one another’s ideas and knowledge, often with Crick playing devil’s advocate. In fact they gossiped and argued so much they were given a room to themselves – to avoid their interrupting the thoughts of their more senior colleagues – within the crowded structure of the old Cavendish Laboratory. The X-ray laboratory, with its heavy machinery and radiation dangers, was located in the basement. Jim and Francis would also share a cheap and cheerful lunch, of shepherd’s pie or sausage and beans, at the local pub, the Eagle – a grubby establishment in a cobblestoned courtyard – where the creative debate would simply continue.
What little they knew about DNA was made even more uncertain by the fact that Crick believed that much of what was generally assumed to be the case with DNA and heredity was almost certainly wrong. It had been this attitude that had got him into trouble with Bragg. It meant that he didn’t even trust the work of his seniors here in the lab. But the real reason behind Bragg’s anger was his resentment of the fact that the chemist, Pauling, had discovered the alpha helix of protein. Meanwhile, Crick was convinced that the reason why the Cavendish had missed out on this was because they were assuming the accuracy of some earlier experimentation on the X-ray interpretation of the skin protein, keratin, which is the main ingredient of our human nails and a raptor’s claws. The way in which Crick’s mind worked can be gleaned from a remembered conversation:
‘The point is [so-called] evidence can be unreliable, and therefore you should use as little of it as you can. We have three or four bits of data, we don’t know which one is reliable … [What if] we discard that one … then we can look at the rest and see if we can make sense of that.’
*
Watson joined the Cavendish in the same year, 1951, in which Linus Pauling published his paper on the protein ‘alpha helix’. This discovery so rattled Watson that all of the time he was working with Crick on the structure of DNA, he was looking over his shoulder in Pauling’s direction.
He had good reason for seeing Pauling as the supreme rival in such an exploration; awarded the Nobel Prize in Chemistry in 1954, Pauling was already being hailed by scientific historians as one of the most influential chemists in history. His master work, though he contributed a great deal more, was to apply a quantum theory perspective to the chemical bonds that bind atoms within the structure of molecules, extending this basic science to the complex organic molecules that are the chemical building blocks of life.
The twentieth century has amazed us with its achievements in astronomy, in which scientists have plotted the stars and galaxies, and the forces, such as black holes, that govern the Universe. Equally important, though not so easily recognised as such by the ordinary man and woman, have been the achievements of the chemists and biochemists in exploring the micro-universe of atoms and molecules. Two forces in particular play a key role in the way that atoms bind to one another to make up life’s particular molecules. One of these is called the covalent bond; the other is called the hydrogen bond. Pauling applied the science of quantum mechanics to the forces involved in these two very different chemical bonds.
We have no need to concern ourselves with the complex mathematics of the applied physics. We just need to grasp the basic mechanics. And where better to look than at the familiar molecule of water.
Everybody knows that the chemical formula for water is H
O. This tells us that a molecule of water comprises one atom of oxygen and two atoms of hydrogen. But how do they link with one another to form the stable compound that we handle and consume every day of our lives? The molecule of water might be compared to a planet, oxygen, with two encircling moons of hydrogen. In such a situation, we can readily imagine how the force of gravity would hold the hydrogen moons to their orbits around the oxygen planet. In molecular terms, the forces holding the two hydrogen atoms to the oxygen atom are called ‘covalent bonds’. At the ultramicroscopic level of atoms, the nucleus of each hydrogen atom contains a single positively charged proton while circling around the nucleus is a single negatively charged electron. Meanwhile, the oxygen atom has eight positively charged protons within its nucleus and eight balancing, negatively charged electrons in orbits around it. These electrons occupy two orbits – two electrons taking up an inner orbit and six taking up an outer orbit. In coming together to form a molecule of water, the two electrons in orbit around each of the two hydrogen nuclei have paired with two of the six electrons of the oxygen outer orbits. The paired electrons share their attraction to the protons of the two parent nuclei, so the paired electrons are now equally attracted to the oxygen nucleus and the hydrogen nuclei. This sharing of attraction creates a stable ‘covalent’ bond between the three atoms, just as gravity created stable orbits for the two moons rotating around our imaginary planet of oxygen.
Hydrogen bonds are something else.
Once again, we might take water as our example. But here we are looking at the chemical interactions between whole water molecules – the H
Os reacting with one another. There are forces of attraction, albeit rather weaker and less stable than covalent bonds, between certain molecules that contain both hydrogen and heavier atoms such as nitrogen, oxygen or fluorine. Since water contains hydrogen and oxygen, these hydrogen bonds can form between molecules of water – it is this sticking together of water molecules that explains the difference between water vapour, or steam, liquid water and solid water, or ice. In ice most of the molecules are attached to one another by hydrogen bonds, to form something like a crystal; in liquid water varying amounts are attached to one another; and in steam, as a result of the addition of energy through heating, the hydrogen bonds linking water molecule to water molecule are broken down but the covalent bonds linking atoms to atoms remain intact.
We see that hydrogen bonds are weak, and thus unstable when heated, but covalent bonds are stable. These same two bonds, covalent and hydrogen bonds, are important ingredients in the structure of organic chemicals such as proteins. And they are also important in the structure of DNA.
Between 1927 and 1932, Pauling published some fifty scientific papers in which he conducted X-ray diffraction studies, coupled with quantum mechanical theoretical calculations, leading him to postulate five rules, known as Pauling’s rules, that would help science to predict the nature of the bonds that held together atoms within molecules. At least three of these rules were based on Bragg’s own work, the purloining of which provoked Bragg to fury. It was now inevitable that there would be ongoing scientific rivalry between the two scientists. Pauling’s work into the nature of chemical bonding was so original, and pioneering, that he was awarded the Nobel Prize in Chemistry in 1954. Meanwhile, this new level of understanding enabled Pauling to visualise the precise shape and dimensions of molecules in three-dimensional space. Working at Caltech, Pauling applied this to the huge molecules of proteins, using the techniques of X-ray diffraction analysis pioneered by the Braggs. He showed, for example, that the haemoglobin molecule – the focus of Perutz’s research – changed its physical structure when it gained or lost an oxygen atom. And Pauling continued to apply his rules to researching the molecular structure of proteins.
Pioneering X-ray pictures of fibrous proteins had been obtained some years before at the University of Leeds by William Thomas Astbury, the physicist who had attended Wilkins’ talk in Naples, but it was assumptions based on these X-ray diffraction pictures that Crick was now questioning at the Cavendish Laboratory. For many years Pauling had tried to apply quantum mechanics calculations to Astbury’s X-ray pictures, but he found that things just didn’t add up. It would take him and two collaborators, Robert Corey and Herman Branson, fourteen years before they made the necessary breakthrough.
All proteins have a primary structure that is made up of an amino acid code, with the letters made up of twenty different amino acids. The chemical bonds that join up the amino acids into the primary chain are called ‘peptide bonds’. Pauling and his collaborators now realised that peptides bonded together in a flat two-dimensional plane – they called this ‘a planar bond’. A problem with outdated equipment had caused Astbury to make a critical error in taking his X-ray pictures: the protein molecules became tilted away from their natural planes, skewing the mathematical extrapolations of their structure. Once they had corrected Astbury’s error, Pauling and co discovered that as the chain of amino acids grew, to form the primary structure of proteins, it naturally followed the shape of a coiled spring, twisting to the right – the so-called ‘alpha helix’. This was the discovery that had excited Watson on his return trip from Naples.
Back in Cambridge, Sir Lawrence Bragg was bitterly disappointed when Pauling’s group beat his to the discovery of the primary structure of proteins. But there was a silver lining to the cloud: Perutz now used Pauling’s breakthrough to reappraise his own work on the haemoglobin molecule, a reappraisal that would solve the structural puzzle of haemoglobin and garner his Nobel Prize in Chemistry in 1963. Pauling’s discovery also alarmed Watson who, from his arrival at Cambridge, had assumed that they had a very knowledgeable and powerful rival in what was now a race to discover the three-dimensional structure of DNA.
*
But the problem, as Crick would point out in their day-to-day sharing of thoughts and incessant debate, was that they couldn’t even assume that Pauling’s data was right. In Crick’s words, ‘Data can be wrong. Data can be misleading.’ So Crick and Watson attempted to construct their physical model with a sceptical eye on prevailing experimental data. To put it another way, they relied just as heavily on creative leaps of their own imagination as on existing experimental data.
Crick and Watson were now asking themselves if DNA, like proteins, had a helical structure, and Watson in particular was convinced that they should also take their cue from Pauling, who liked to construct three-dimensional models of the molecules he was attempting to envisage. To do so they would have to think, as Pauling did, about the atomic structures that made up the chemistry of DNA – to fit the molecules, with their component atoms, and the bonds between them, into a complex three-dimensional jigsaw. They knew that they were dealing with the four nucleotides – guanine, adenine, cytosine and thymine – together with the molecule of the sugar, called ribose, and the inorganic chemical, phosphate, all of which, when correctly fitted together, must somehow make up the mysterious three-dimensional jigsaw puzzle.
Two relevant questions now loomed. Firstly, if the structure was helical, what kind of helix was involved? And secondly, where did the phosphate molecule fit into the structure? Calcium phosphate is the mineral of bones, of shells, of rocks formed from the remains of living marine organisms – limestone. The presence of phosphate suggested some kind of strengthening of the DNA chain – a chemical scaffold – maybe a spine? But where did this spine lie in relation to the presumptive and as yet unknown spiral? And where, or how, did the sugar fit in? The code itself must surely lie with the nucleotides, acting perhaps as something like letters. Each was a key ingredient, but how on earth did the whole thing assemble in a way that made sense?
An important clue must come from the X-ray diffraction patterns. That meant they needed the help of Maurice Wilkins and Rosalind Franklin – ‘Rosy’, as Watson referred to her in his autobiography – who were conducting X-ray analyses of DNA fibres at the King’s College London laboratory.
*
Rosalind Elsie Franklin was born in London to a prosperous Jewish family in 1920. From an early age she showed both a brilliantly incisive mind and the stubbornness necessary to make a distinguished mark for herself. She also showed an aggressively combative side to her personality that might prove a mixed blessing in overcoming the prevailing prejudices against Jews in society, as well as against women being in higher education and the scientific workplace. It didn’t help that her father, who appeared to be a similarly combative character to his daughter, opposed her notion of a career in science. In her second year at Newnham College, Cambridge, he threatened to cut off her fees, urging that she switch to some practical application in support of the war effort. Only when he was dissuaded by her mother and aunt did he relent and allow her to continue her course.
Franklin studied physical chemistry, which involved lectures, extensive reading and laboratory experience in physics, chemistry and the mathematics that applied to these disciplines. One of the mandatory texts she read was Linus Pauling’s The Nature of the Chemical Bond.
The youthful Rosalind Franklin was disappointed when she ended up with a good second, and not a first, ‘bachelor’s’ degree in 1941. Even then, such was the lingering prejudice against female graduates in science that she was forced to wait in an unseemly uncertainty, one shared with all previous female graduates of Newnham, until her due qualification was formally granted, retrospectively, in 1947.
Like Francis Crick, Franklin was seconded to National Service during the Second World War, studying the density and porosity of coal for a PhD, in which she helped to classify different types of coal in terms of fuel efficiency. Post-war, she followed this up with a research stint working under the direction of Jacques Mering at the Laboratoire Central des Services Chimique de l’Etat, in Paris. Here, Mering introduced her to the world of X-ray crystallography which he used to study the structure of fibres, such as rayon. ‘With his high tartar cheekbones, green eyes and hair combed rakishly over his bald spot’, Franklin was surprised to discover that Mering was Jewish, as well as being ‘the archetypal seductive Frenchman’. The still youthful, and perhaps naïve, Rosalind Franklin appears to have fallen in love with Mering, who was already married, but whose wife was ‘nowhere in evidence’.
Brenda Maddox, one of Franklin’s biographers, would draw attention to the fact that Franklin’s most imaginative and productive research was conducted when she was teamed up with male scientists of Jewish background. Mering also appeared to be attracted to the trim, slender young woman, with the lustrous dark hair and glowing eyes. They would spend entire days and on into the evenings deep in discussion and argument over likely meanings of X-ray plates and atomic structures.
However, Franklin’s infatuation with Mering would be painfully halted when, in January 1951, she took up a post as research associate at King’s College London in the Medical Research Council Biophysics Unit, directed by John Turton Randall. Her appointment happened to coincide with a major post-war rebuilding within the department, designed to accommodate new ambitions within the nascent field of biophysics. The precise nature and purpose of her appointment has since become the subject of debate. In part some confusion has arisen because Randall changed the scope of her appointment in between first confirming it and Franklin taking up the post. She had initially agreed to carry out X-ray diffraction studies of proteins, but Randall wrote to her before she took up her appointment, suggesting that she change direction to the study of DNA. According to Maurice Wilkins, this was at his suggestion. Whether at Wilkins’ suggestion or Randall’s own idea, Franklin agreed. She was offered the assistance of a promising graduate student, Raymond Gosling, to work with. But there was an inherent problem with this new direction.
Wilkins, who was Deputy Director of the MRC Unit based at King’s College, was the same scientist who had first lit the fuse of inspiration for Watson in the 1950 Naples lecture. Wilkins had initiated the research into DNA in the department, but happened to be deputising once again for Randall in America at the time of Franklin’s appointment. Up to now Gosling had been working with Wilkins on DNA; even after his return from America, Randall failed to inform Wilkins about the terms he now proposed for Franklin’s job description. This led to what Franklin’s later research colleague, Aaron Klug, would describe as ‘an unfortunate ambiguity about the respective positions of Wilkins and Franklin, which later led to dissension between them and about the demarcation of the DNA research at King’s’.
This is a short quote from the typed letter from Randall to Franklin, specifying her working conditions:
… as far as the experimental X-ray effort is concerned there will be at the moment only yourself and Gosling, together with the temporary assistance of a graduate from Syracuse, Mrs. Heller …
While this clearly suggests that Franklin was expected to take on the X-ray diffraction work, the qualification ‘at the moment’ is too vague to interpret. But there is nothing in this letter to suggest that Franklin should ignore the work performed by Wilkins, or that she should refuse to collaborate with the rest of the department in her approach to the DNA problem.
Wilkins, working with Gosling, had initiated the X-ray diffraction studies on DNA in the department, and in particular obtaining the best resolution diffraction photographs that existed up to this date. They had demonstrated a key property of DNA – that it had a regular, crystal-like molecular structure. In Paris Franklin had learned, and improved upon, X-ray diffraction techniques for dealing with substances of limited order. But even Klug, an ardent supporter of Franklin, admitted that in relation to the work conducted by Franklin in Paris, ‘It is important to realise … Franklin gained no experience of such formal X-ray crystallography.’
Back in early 1950 Wilkins had complained of poor-quality X-ray apparatus that was not designed for the scrutiny of exquisitely fine fibres. At his suggestion, the department had purchased a new and better-quality X-ray tube to be set up in the basement, but it had lain there for a year or more unused while Wilkins was distracted by the multiple tasks that fell to a busy deputy director of the unit. On her arrival, Franklin, not unnaturally, believed that she was there to take over the DNA work as her personal project. However, the returning Wilkins expected that Franklin had been brought in as his collaborator, to take up the research from where he had already developed it. He would subsequently admit that he was unqualified to take the X-ray diffraction work further and needed exactly such a dedicated and qualified collaborator. ‘That’s why we hired Rosalind Franklin.’
Unfortunately, Franklin and Wilkins now disagreed as to her role. Even so, rancour was neither necessary nor inevitable between the two scientists, personally or scientifically. These difficulties, provoked by Randall’s vagueness, might have been readily overcome with goodwill on both sides, but Franklin, in the opinion of both her biographers, was not inclined to cooperate.
Much has been written about prejudicial attitudes to women in science at this time. In particular an American journalist, and personal friend of Franklin’s, Anne Sayre, would write a biography of her in which she suggested that King’s College was particularly unfriendly to female scientists, with Franklin struggling to assert her presence in a domain that was almost exclusively male. But when another American journalist, Horace Freeland Judson, looked into this claim, he discovered that of the 31 staff working at King’s at this time, eight were female, including some working in a senior position in Franklin’s unit. A second biography of Franklin, by Brenda Maddox, confirmed that women were, on the whole, well treated at King’s College. Crick made the same point in his biography – and Crick had come to know Franklin well in the years following the DNA discovery. Even in Sayle’s more trivial complaint – that the main dining room was exclusively forbidden to women, who were thus precluded from lunchtime conversation – is misleading. There were two dining rooms. One was limited to men, but this, in the main, was used by Anglican trainees. The main dining room, used by the departmental staff, including Randall himself, was open to all.
The frosty relationship between Wilkins and Franklin was not the result of anti-female prejudice – it even seems unlikely to be the result of Randall’s peculiar wording in the letter – but it appears to be more directly related to a personality clash between the two scientists. Of the two, only Wilkins ever seems to have made any attempt at compromising. He asked other colleagues what he should do, but Alexander (Alec) Stokes, his closest colleague, was even meeker than he was. In Brenda Maddox’s opinion, the two should have got on well; Wilkins was gentle in manner and, despite his lack of self-confidence, was attractive to women. He was mathematically fluent and immersed in the very problems that concerned Franklin. But ‘confrontation’, in Maddox’s words, ‘was Franklin’s tactic, whenever cornered’. In an earlier confrontation with her professor, R. G. W. Norrish, when working on a postgraduate research project at Cambridge, she would confide, ‘When I stood up to him … we had a first-class row … he has made me despise him so completely I shall be quite impervious to anything he may say in the future. He gave me an immense feeling of superiority in his presence.’
Sayre, who championed her friend, would admit that Franklin’s ogrish depiction of her professor was unkind and inaccurate. Professor Norrish was awarded the Nobel Prize in Chemistry in 1967.
Sayre had a correspondence with Norrish in which she described Franklin as ‘highly intelligent … and eager to make her way in scientific research’, but also ‘stubborn, difficult to supervise’ and, perhaps most tellingly, ‘not easy to collaborate with’. In Maddox’s opinion, ‘If Rosalind had wished, she could have twisted Wilkins around her little finger.’ The fact is she had no wish to collaborate with him. This left Wilkins isolated locally so instead he turned to Crick and Watson at Cambridge. It also meant that Franklin was equally isolated. To the commonsensical Crick, this may have been a crucial factor when it came to working out the molecular structure of DNA. ‘Our advantage was that we had evolved … fruitful methods of collaboration, something that was quite missing in the London group.’
In that same year of Franklin’s appointment, just before Wilkins headed for America, he asked his colleague, Alec Stokes – another Cambridge-educated physicist – if he could work out what kind of diffraction pattern a helical molecule of DNA would project onto an X-ray plate. It took Stokes just twenty-four hours to do the mathematics, largely figuring it out while travelling home on the commuter train to Welwyn Garden City. A helical model fitted very closely with the picture Gosling and Wilkins had obtained in their diffraction pictures of DNA. It would appear that if anybody first confirmed that DNA had a helical structure, the credits must surely include Wilkins, Gosling and Stokes – the latter would subsequently lament that, in retrospect, he might have merited 1/5000th of a Nobel Prize.
In November 1951, Wilkins told Watson and Crick that he now had convincing evidence that DNA had a helical structure. Watson had only recently heard Franklin say something similar in a talk about her research during a King’s College research meeting. This inspired Watson and Crick to attempt their first tentative three-dimensional model for DNA.
But where to begin?
Taking their cue from Linus Pauling, Watson and Crick decided that they would attempt to construct a three-dimensional physical model of the atoms and molecules that made up DNA with their covalent and hydrogen bond linkages to one another. On the face of it, the structure was made up of a very limited number of different molecules. There were the four nucleotides – guanine, adenine, cytosine and thymine – but they also knew that the structure contained a sugar molecule, deoxyribose, and a phosphate molecule. The phosphate was likely to be playing a structural role, perhaps holding the thread together, much as phosphate is a key structural component of our bony human spine. In the colloquium at King’s, attended by Watson, such was his lackadaisical absence of focus that he completely missed the importance of Franklin’s statement that the phosphate-sugar ‘spines’ were on the outside, with the coding nucleotides, the GACT, on the inside. As usual, he had eschewed making notes. All that seemed to intrigue Watson was the fact that the King’s people were uninterested in the model-building approach developed, with such aplomb, by Pauling.
In 1952 Franklin appears to have undergone a drastic change of heart in her own thoughts on the structure of DNA. She had in her possession a brilliantly clear X-ray picture of DNA, taken by Gosling, that clearly showed a helical structure to the molecule. She called this her ‘wet form’, and also her ‘B form’. But she had even clearer pictures of a different structure of the same molecule in its ‘dry form’, or ‘A form’, that did not appear to suggest a helix. The contrast between the two forms caused Franklin to dither as to whether the DNA molecule was helical. There is a suggestion that she may have asked the opinion of an experienced French colleague, who advised her to place her bets on whichever form gave the clearest pictures. She must have been altogether aware of the advice her ignored colleague, Wilkins, would have given. Unfortunately, she ended up putting the B form into a drawer, meanwhile focusing most of her research over that year into the A form.
Early that same year Watson and Crick made a first attempt at building a triple-stranded helical model of DNA, with a central phosphate-sugar spine. When Wilkins brought Franklin and Gosling up to Cambridge to view the model, they broke out into laughter. The model was absolute rubbish. It did not fit at all with the X-ray diffraction predictions. Thanks to Watson’s lackadaisical focus, and his failure to take notes at Franklin’s colloquium, he had made the cardinal error of putting the phosphate-sugar spine at the dead centre of their helix and not on the outside, as Franklin and Gosling had clearly deduced.
Sayre, who rightly defended Franklin from the egregious caricature depicted by Watson’s book, loses track of the contribution of Wilkins and Gosling. It is true that Franklin and Gosling had produced some of the clearest pictures yet of the B form of DNA, pictures of such clarity that they did come astonishingly close to the truth of its molecular structure. But then, confused for a year by the two seemingly different patterns of the A and B forms, Franklin veered away from her own earlier conclusions and for a year she took the view that DNA wasn’t helical at all. Sayre appears to refute this, but Gosling would subsequently confirm Wilkins’ account of how, on Friday 18 July 1952, Franklin goaded Wilkins with an invitation to a wake. The invitation card announced, with regret, the death of the DNA helix (crystalline) following a protracted illness. ‘It was hoped that Dr M. H. F. Wilkins would speak in memory of the deceased.’ At the time Wilkins assumed it was typical of Gosling’s sense of humour. But many years later he would discover that it was Franklin who had written the card, and it confirmed her refutation of any helical structure of DNA in that confused year.
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Frank Ryan
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Жанр: Зарубежная образовательная литература
Язык: на английском языке
Издательство: HarperCollins
Дата публикации: 16.04.2024
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О книге: How could a relatively simple chemical code give rise to the complexity of a human being? How could our human genome have evolved? And how does it actually work?Over the past 50 years we have deciphered the inner workings of the human genome. From the basic structure of DNA through to the complete sequence of the code, what first appeared to be simple is actually a complex and beautiful three-dimensional world that makes each of us who we are.In The Mysterious World of the Human Genome acclaimed science writer Frank Ryan leads us through the most exciting scientific discoveries of the last 50 years, revealing how this science has unlocked the cure of some genetic diseases, developed the use of DNA in forensic science and paternity testing, helped us trace our ancestors and provided a definitive map for the movement of humans out of Africa. This scientific journey has had a profound impact on our understanding of the evolution of life itself, through the role of the most ancient of organisms in our basic biology all the way to the revelation that our most recent ancestor, Homo neanderthalensis, lives on in many of us.In the ever more complicated world of the human genome, this is the first book to explain how the human genome actually works as a whole and how that knowledge will have a profound effect on our understanding of where we have come from and where we are likely to be going in the future.