Much later, when the true magnitude of ‘something important’ had sunk in, some of those present reported a more dramatic end to the afternoon: Alfred Mirsky, pushing his way to the front of the room to pour vitriol on Avery’s fatuous claim that DNA could transform pneumococci. But these were false memories, conjured up by what Mirsky did subsequently.
Most members of the audience had only vague recollections of the first time that scientists were shown evidence that DNA is the material of heredity.
The twenty-page paper by Drs Avery, MacLeod and McCarty came out in the Journal of Experimental Medicine on 1 February 1944. They described the journey of ‘heart-aches and heart-breaks’ in dispassionate scientific prose, with rare flashes of poetry such as the ‘silky sheen’ that appeared on stirring a strong solution of transforming principle. Their conclusion was clear: ‘The evidence presented supports the belief that a nucleic acid of the desoxyribose type is the fundamental unit of the transforming principle of the Pneumococcus Type III.’ But you could be forgiven for failing to grasp that this was a monumental landmark in the history of biology.
The paper’s publication coincided with the liberation of Stalingrad, which helped to ensure a muted reception. When the reprints arrived, Maclyn McCarty sent one to his mother with the heartfelt inscription, ‘This is it, at long last.’ More perceptively, Peyton Rous filed his editor’s copy away, not under ‘Bacteriology’, but under ‘Genetics’.
And Alfred Mirsky began to pile up the ammunition for an all-out assault on Avery’s claim that DNA had anything to do with heredity.
End of an era
We can only speculate about how Fred Griffith might have reacted on seeing where ‘the significance of pneumococcal type’ was leading. Most probably, he would have preferred shade to limelight and would have refused all invitations to talk about his revolutionary discovery.
Soon after war was declared in September 1939, the laboratory in Dudley House had acquired a new identity. As the Emergency Public Health Laboratory (EPHL), its brief now included war-wound infections and (God forbid) germ warfare. At first, the daily routine changed little. When imports of agar jelly (obtained from Japanese seaweed) dried up, culture plates were filled with an extract of dulse collected from the shores of Wales.
The team at Dudley House carried on as usual when the Blitz began in October 1940. William Scott’s elder son went to fight in France, the rest of the family remaining in Dulwich. Fred Griffith also stayed put, even though Eccleston Square was close to the eminently bombable Victoria Station. By then, he was irreversibly set in his ways: a sixty-year-old bachelor who had spent half his lifetime working at the same bench and alongside the same friend and colleague. He refused point-blank to move ‘for any German’.
March 1941 was an exciting month for Scott, and a grim one for Griffith. Scott was appointed Director of the EPHL, while Griffith was preoccupied with his brother’s deteriorating health. Stanley died just before Easter and Fred was devastated. Quite naturally, the man who had been Griffith’s best friend for three decades did his best to cheer him up. After work on Wednesday 16 April 1941, Scott went home with Griffith to join Fred’s niece, housekeeper and dog in the house in Eccleston Square.
That was not the worst night of the Blitz, but as dawn broke, it was obvious that London had taken a terrible pounding. In Pimlico, where the first bombs had fallen just before midnight, nearly 150 people were killed and over 500 injured. South of Victoria Station, three houses in Eccleston Square had taken direct hits. From the ruins of one, a young woman and an Irish terrier were dug out alive. The other three occupants of the house – two men and a woman, all aged between fifty and sixty – had been killed instantly.
William Scott, the recently appointed Director of the EPHL, was conspicuously mourned by the Journal of Pathology, which noted that ‘The gap in our ranks left by Scott’s death will be very difficult to fill.’ The same journal devoted four pages to the late Dr Griffith – but this was Stanley, not Fred. The British Medical Journal insulted the memory of William Scott and Fred Griffith by lumping them together in a joint obituary as ‘Medical officers, Ministry of Health’, and dismissed Griffith’s career as ‘working in the pathological laboratories from 1911 onwards’. Only the Lancet mentioned that Griffith had achieved the ‘transformation of pneumococcal types under certain circumstances’. He had been slow to publish, but then ‘he always took the line, “Almighty God is in no hurry – why should I be?”’
Fred Griffith died without knowing that he had discovered something which would transform the understanding of life on Earth. He might also have been surprised to learn that, after news of his death reached New York, the great Oswald Avery cleared a space on his cluttered desk for a framed photograph. It was a snapshot of a man with his dog, taken on the South Downs above Brighton, England, in the summer of 1936, and it stayed on Avery’s desk for the rest of his time at the Rockefeller.
* This strength (1 molar) is about twice as salty as sea-water, and seven times more concentrated than the sodium levels in human plasma.
† In everyday units, enough culture medium to fill the petrol tanks of 200 domestic cars would produce a teaspoonful of transforming principle.
17
TIDYING UP
Avery was quietly confident about their discovery months before he and McCarty wrote their paper, but chose not to tell the man doing all the work. Instead, he treated two outsiders to a detailed review of McCarty’s findings – perhaps to gauge reactions or check the deductions that led to DNA. The first was the eminent immunologist Macfarlane Burnet, who visited Avery in March 1943. Burnet initially wondered whether Avery had begun to ‘live in the past’ – but then was bowled over by Avery’s ‘extremely exciting discovery’. He wrote to his wife that this was ‘nothing less than the isolation of a pure gene in the form of desoxyribonucleic acid’.
Shortly after, Avery was invited to Sunday lunch out in the suburbs. His host was Alvin Coburn, an up and coming microbiologist who had always been alert to the new and unusual – for example, at the International Microbiology Conference in London in 1936, where everyone else had written off Fred Griffith because his talk was so awful. Coburn, however, was intrigued and visited Griffith at his weekend house near Brighton. It was there that Coburn took the snapshot of Griffith with his dog, which he presented to Avery because ‘it belongs alongside your work’.
Avery arrived for lunch with a box of sherry chocolates (a rare gift in those days of rationing) and a broad smile that Coburn interpreted as saying, ‘I have discovered a phenomenon of Nature so exquisitely beautiful that I dare not talk about it except to those with whom I commune.’ After lunch, the two men absented themselves and Avery launched into the ultimate Red Seal recital: a three-hour travelogue describing the journey to DNA. Coburn was mesmerised. Afterwards, he wrote to ‘Dear Fess’, thanking him for the chocolates and ‘the most inspiring experience that I have had in medicine’.
Reception party
All this euphoria prepared Avery badly for what actually happened when the Journal of Experimental Medicine published their landmark article in February 1944. The paper was barely noticed by their peers, hurrying past with their heads down and concentrating on their own paths of enquiry. It was like a prolongation of the peculiar silence which had greeted Avery’s seminar at the Rockefeller and which could have signalled incomprehension, disinterest, disbelief or mistrust.
For months, the only person to comment openly was Alfred Mirsky, ‘the principal public sceptic’, who had begun sniping at Avery even before the paper came out. According to Mirsky, Avery’s team were amateurs who had blundered into a field they did not understand. Their claim that DNA determined the characteristics of a living organism was ridiculous, because any expert on DNA could tell them that its structure was too banal. The transforming principle had to be a protein, which they had not been clever enough to find. The criticisms were repeated in the paper which Mirsky and Pollister wrote about their joint exp
eriments with Avery and McCarty. Mirsky was ‘indebted to Dr McCarty’ for showing that ‘pneumococcal chromosin’ had the power to transform. However, this in no way proved that DNA was responsible, because chromosin consisted of DNA combined with nuclear proteins. ‘It is not yet known,’ he wrote, ‘which the transforming agent is – a nucleic acid or a nuclear protein. To claim more, would be going beyond the experimental evidence.’ Put bluntly, ‘Anyone who has prepared nucleic acids knows that traces of protein probably remain in even the best preparations.’ Avery’s supposedly protein-free preparations could contain 1–2 per cent of protein – easily enough to conceal the real transforming protein.
McCarty ‘never had a clear understanding of how and why the estrangement came about’, but Levene’s tetranucleotide hypothesis was still hanging in the air, like the ghost of Hamlet’s father, returning at awkward moments to interfere with the plot. Mirsky may also have resented the fact that these chemically uneducated interlopers had stumbled across something bigger than he had ever discovered. And he might have wanted revenge because Avery had not properly acknowledged his expert input.
Over the next couple of years, McCarty attacked Mirsky’s claim that transformation was caused by an undetected contaminating protein. As each chunk of evidence threatened to land on Mirsky, he scuttled sideways like a crab and desperately tried to find a new objection. McCarty got rid of histones, protamines and all measurable proteins; Mirsky insisted that the ‘genetic’ protein was still in there, maybe chemically altered during extraction so that it would not be detected. Finally, McCarty isolated DNase, a newly discovered enzyme which specifically breaks down DNA, from extracts of beef pancreas and showed that this wiped out the power to transform. Mirsky batted that one away too. McCarty’s DNase was obviously contaminated with a protein-digesting enzyme, which had destroyed the all-important genetic protein.
Mirsky never revealed whether his real bête noire was Avery or the notion that DNA = genes, but he continued his tirades for years, even after Avery retired and the tetranucleotide hypothesis had died. He could easily have executed a graceful U-turn, citing the noble precedent of ‘When the facts change, I change my mind.’ Instead, Mirsky stuck to his guns: a clever man but a flawed scientist, who was prepared to wreck his own reputation for the dubious gratification of doing a colleague down.
Avery had another enemy, as influential and as toxic as Mirsky – himself. Like Fred Griffith, Avery made himself an unclubbable outsider who remained ‘completely aloof’ from the bacteriological fraternity. He was also unknown to another important club – the geneticists – and he was totally ignorant about them. Avery was ‘not as broadly informed as a scholar as one might assume from his achievements and fame’ and made no effort to update his knowledge of genetics – dating from his medical student days, before Mendel and the Fly Room appeared on the curriculum.
Nonetheless, Avery’s experiments caught the eye of Theodosius Dobzhansky, one of the brightest of the stars who joined Herman Muller’s lab at Caltech. In the second edition of his masterpiece Genetics and the Origin of Species (1941), Dobzhansky wrote: ‘If this transformation is described as a genetic mutation – and it is difficult to avoid so describing it – we are dealing with authentic cases of induction of specific mutation by specific treatments – a feat which geneticists have vainly tried to accomplish in higher organisms.’
However, Dobzhansky did not think that transformation was the direct transfer of genetic material; instead, he argued that the transforming principle was a powerful chemical inducer of mutations, which somehow hit the same target every time. Herman Muller was also unpersuaded, partly because of Mirsky’s criticisms, and could not decide whether genetic ‘specificity’ might reside in DNA or in the associated proteins.
Long goodbye
Avery’s retirement was marked in December 1944 by a special dinner at the Harvey Club, featuring an affectionate song (to the tune of ‘It Ain’t Necessarily So’) which began, ‘Little Avery was small, but oh my!’ Thereafter, Avery was gloomy and difficult company, sitting in silence at the bench while McCarty tried to hide his irritation and get on with the experiments. Avery made things worse by keeping McCarty in the dark. While leafing through Science, McCarty discovered that Avery had lectured on DNA and transformation at a major national meeting; and later, that he had been awarded the Gold Medal of the New York Academy of Medicine for his breakthrough, which had ‘very far-reaching implications for the general science of biology’.
In spring 1946, McCarty won his first recognition as a researcher in his own right, with the prestigious Eli Lily Award of the Society of American Bacteriologists. This was given to the most outstanding investigator under the age of thirty-five; McCarty delivered his prize lecture in Detroit on 24 May, two weeks before the deadline birthday. He told it as it was: DNA mediated transformation, and the phenomenon would prove important in the ‘field of genetics and in virus and cancer research’. His lecture went down extremely well. So did the ‘handsome’ silver medal and cheque for $1,000, with which he treated his wife to a piano. Later, McCarty discovered that Avery had nominated him for the award.
In all, McCarty stayed on with Avery for a couple of years after their big paper came out. He was confident that ‘genes were made of DNA, and that this would ultimately be accepted’, but did not see his future in making that happen. Neither did Tom Rivers, who lined him up to direct research into the cause of rheumatic fever.
McCarty’s last act in Avery’s lab was to present a paper at the Cold Spring Harbor Symposium in June 1946. Cold Spring Harbor had come a long way since its birth in 1910 as the Eugenics Foundation, and its annual symposia on quantitative biology brought together scientists from different disciplines to look at a hot topic in the round. The subject in 1946 could have been chosen specifically for Avery: ‘Heredity and variation in micro-organisms’. McCarty went with Harriett Taylor, ‘bright, talented and personable’ and a PhD in yeast genetics, who had recently joined the lab. As usual, Avery – who had originally been invited – stayed away.
The symposium was bristling with geneticists and experts on the peculiar ‘bacteriophage’ viruses which prey on bacteria. McCarty took a bullish line: ‘the active substance responsible for transformation is a specific nucleic acid of the desoxyribose type’. The message should have been clear and exciting, but McCarty was buttonholed afterwards by a ‘hard case’ geneticist who insisted that ‘you fellows’ had shown that DNA was not responsible, and told him to ‘get to work and find out what really is’.
On 1 July 1946, McCarty left behind two distinct phases of his life. He changed out of naval uniform into civilian clothes, and he quit Avery’s lab. His personal account makes no mention of regrets over either transition. For a while, he kept in touch with the DNA-transformation story. In early 1949, he was invited to give a guest lecture at his alma mater, Johns Hopkins. The large auditorium was packed when he arrived, with people standing at the back. McCarty’s talk was the second of the evening; immediately after the first, which reported a novel treatment for sea-sickness, almost everyone left.
Over and out
McCarty’s successors were Harriett Taylor and Rollin Hotchkiss, an experienced bacteriologist and biochemist. Both strengthened the case for DNA, but most persuasively after Avery had left the Rockefeller. Taylor showed that other characteristics of pneumococci – such as the appearance of their colonies – could be interchanged, just like type and virulence, and that DNA was again responsible. This argued strongly for DNA being the genetic material, and against Dobzhansky’s notion that it was a chemical which induced a constant mutation. Taylor’s time in Avery’s lab was curtailed because of the 1946 Cold Spring Harbor Symposium, where she met Boris Ephrussi, a brilliant and charming Drosophila geneticist from Paris. She joined him there the following year; for the rest of her career, Dr Taylor-Ephrussi was constantly reminded of her inspiration, by the framed photograph of Oswald Avery which hung above her desk.
Rollin
Hotchkiss put great energy into repelling Mirsky’s continuing crusade against DNA and Avery. He picked up where McCarty had left off, by showing that transformation was abolished by the newly available crystalline DNase, so pure that it could not be contaminated with protein-degrading enzymes. His greatest coup was to measure the amounts of the four bases (adenine, guanine, cytosine and thymine) in DNA from different sources, and to show that the base composition of pneumococcal DNA (the transforming principle) bore no resemblance to that of DNA extracted from calf thymus. Better still, neither source of DNA contained equal amounts of each base, as predicted in Levene’s tetranucleotide. As well as hammering another nail into the tetranucleotide’s coffin, this was the first hint that DNA possessed the structural variability which was an absolute necessity for any substance purporting to be the stuff of genes. Unfortunately, Hotchkiss presented his findings at a meeting in Paris, which published its proceedings a year later in a minor French journal. If he had set out to bury his results, he could hardly have done a better job.
And Mirsky was still on their trail, as convinced of his own rectitude as a witchfinder in Salem.
After retiring, Avery continued much as before for another three years, loosely supervising McCarty, Taylor and Hotchkiss. During these twilight years, Avery collected accolades that signal a world-class career: 1944 – Foreign Membership of the Royal Society of London, and an Honorary Doctorate from Cambridge; 1946 – the Copley Medal of the Royal Society, its highest distinction, reserved for the likes of Darwin, Pavlov and Einstein; 1947 – the Lasker Award for basic medical research (on pneumococci, not DNA). Normal people would have luxuriated, if not gloried, in these honours – but not Avery. The only ceremony he attended was for the Lasker Award, held in New York.
Unravelling the Double Helix Page 24