Free Life's Greatest Secret by Matthew Cobb

therefore the main component of genes. To prove their point, production of the stuff had to be stepped up – it took 200 litres of bacteria to produce just 40 milligrams of stringy white precipitate. By this stage, McCarty had been called up to active duty by the Naval Reserve research unit. Feeling he should do something related to the war effort, McCarty asked to be put on a more practical project relating to disease treatment, but was told not to worry and to return to Avery’s lab – the main difference that his call-up made was that he now went to the lab in uniform.
    In April 1943, Avery’s report to the Rockefeller Institute Board explicitly framed the problem of transformation in terms of genes for the first time. The transforming principle ‘has been likened to a gene’, Avery wrote, and the polysaccharide was like ‘a gene product’. He explained:
    The genetic interpretation of this phenomenon is supported by the fact that once transformation is induced, … both capsule formation and the gene-like substance are reduplicated in the daughter cells.
    Nevertheless, he wrote in typically cautious style that proof was still lacking and that all his conclusions were provisional:
    If the present studies are confirmed and the biologically active substance isolated in highly purified form as the sodium salt of desoxyribosenucleic acid actually proves to be the transforming principle, as the available evidence now suggests, then nucleic acids of this type must be regarded not merely as structurally important but as functionally active in determining the biochemical activities and specific characteristics of pneumococcal cells.
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    Shortly afterwards, on 13 May 1943, Avery began writing a letter to his younger brother, Roy, who was professor of microbiology at Vanderbilt University in Nashville, Tennessee. While most people called Oswald Avery ‘Fess’, to Roy – 15 years younger – Avery was simply ‘Brother’. 16 In the letter, written in spidery handwriting, Fess told Roy about his plans to retire and join him in the South: ‘If this War wasn’t on I tell you frankly I would liquidate my affairs here and start for Nashville this fall’, he wrote. Two weeks later, on the night of 26 May, Avery finally got round to completing what he called ‘a rambling epistle’. In this second part, he broke with the personal and slightly weary tone of the opening section and explained to Roy exactly what he and his group had discovered. Avery first reminded his brother about Griffith’s discovery of transformation and the steps that his laboratory had taken in the 1930s to identify the chemical basis of the phenomenon. Then he allowed an element of triumph to creep into his description of the hard work that was involved, before his habitual caution reasserted itself:
    Some job – and full of heartaches and heart breaks. But at last perhaps we have it … the substance is highly reactive and on elementary analysis conforms very closely to the theoretical values of pure desoxyribose nucleic acid (thymus type). Who could have guessed it? … We have isolated highly purified substance of which as little as 0.02 of a microgram is active in inducing transformation … this represents a dilution of 1 part in a hundred million – potent stuff that – and highly specific. This does not leave much room for impurities – but the evidence is not good enough yet.
    Avery then explained the implications of his discovery, showing that he fully understood the importance of what he had found:
    If we are right, and of course that’s 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