chromosome complement at different phases was what would be expected of a gene – nothing like this had been found for any protein. In bacteria, plants and animals, Boivin argued, ‘each gene can, in the final analysis, be considered as a macromolecule of DNA.’ 31
This was one of Boivin’s last lectures. The cancer he had been suffering from returned and he died in July 1949. In the meantime, doubts began to be raised about his reports on transformation in
E. coli
– researchers in the US were unable to replicate his findings, and his original strains were lost. 32 Despite – or perhaps because of – Boivin’s bold statements and prophetic vision, an air of disbelief accumulated around his discoveries. This took years to dissipate – his findings were eventually confirmed in the 1970s, and his vision of the nature of heredity and the future of biology were also shown to be true. 33
*
By the end of the 1940s, support for the hypothesis that DNA had a fundamental role in heredity had grown much stronger. In the summer of 1950, the cell biologist Daniel Mazia gave a lecture at Woods Hole Marine Biology Laboratory that summed up many people’s thinking. Mazia could not be absolutely certain that genes were made of DNA, but it certainly looked that way: ‘The “physical basis of heredity” is something in the chromosome which may or may not be DNA, but which follows DNA for all practical purposes’, he said. 34 Following Boivin, Mazia outlined four criteria that had to be met by what he called the vehicle of heredity, whatever its chemical composition might be. There had to be the same amount in every diploid cell of a given species, that amount should double just before ordinary cell division, and it should be halved during the creation of haploid sex cells. It should be stable, it should be capable of specificity and it should be able to be transferred from one cell to another and act like a gene. Proteins failed at the first hurdle – there was no evidence that the levels of protein in cell nuclei were the same in all tissues of an organism. All that proteins had going for them was that they were known to be complex. Both Chargaff and Gulland had suggested that nucleic acids could vary by the sequence of the bases, perhaps providing a source of complexity. While still not excluding the possibility that proteins were involved, Mazia concluded: ‘DNA is the most likely candidate so far for the role of the material basis of heredity.’ 35
A couple of months earlier, in April 1950, Mazia had chaired a session at a special conference on the biochemistry of nucleic acids, held at the US Atomic Energy Commission’s Oak Ridge Laboratory in Tennessee. Among the speakers was Arthur Pollister, who with Mirsky had criticised Avery’s conclusions two years earlier. Pollister was changing his tune; he enthusiastically reported the data from Boivin’s laboratory that showed that the amount of DNA was constant in all diploid cells of a given species, before discussing the idea of a ‘DNA-gene’ and raising the possibility that the chemical structure of the gene was within reach. Nevertheless, Pollister was not completely convinced: the complexity of gene function led him to suggest that ‘important genic components other than DNA remain to be discovered.’ 36
Another speaker at the Oak Ridge meeting was Erwin Chargaff, who was acquiring some of the most telling evidence in favour of Avery’s conception of the role of DNA. Chargaff had been an early supporter of Avery’s hypothesis, and in 1950 he presented data on the precise base composition of nucleic acids, using paper chromatography to identify the bases by weight. He found that the proportion of the different bases was constant in all tissues of any species, but differed wildly between species. As Chargaff pointed out, these data disproved the tetranucleotide hypothesis, to the extent that anyone still thought it was true. 37 DNA was clearly not boring.
The
This was one of Boivin’s last lectures. The cancer he had been suffering from returned and he died in July 1949. In the meantime, doubts began to be raised about his reports on transformation in
E. coli
– researchers in the US were unable to replicate his findings, and his original strains were lost. 32 Despite – or perhaps because of – Boivin’s bold statements and prophetic vision, an air of disbelief accumulated around his discoveries. This took years to dissipate – his findings were eventually confirmed in the 1970s, and his vision of the nature of heredity and the future of biology were also shown to be true. 33
*
By the end of the 1940s, support for the hypothesis that DNA had a fundamental role in heredity had grown much stronger. In the summer of 1950, the cell biologist Daniel Mazia gave a lecture at Woods Hole Marine Biology Laboratory that summed up many people’s thinking. Mazia could not be absolutely certain that genes were made of DNA, but it certainly looked that way: ‘The “physical basis of heredity” is something in the chromosome which may or may not be DNA, but which follows DNA for all practical purposes’, he said. 34 Following Boivin, Mazia outlined four criteria that had to be met by what he called the vehicle of heredity, whatever its chemical composition might be. There had to be the same amount in every diploid cell of a given species, that amount should double just before ordinary cell division, and it should be halved during the creation of haploid sex cells. It should be stable, it should be capable of specificity and it should be able to be transferred from one cell to another and act like a gene. Proteins failed at the first hurdle – there was no evidence that the levels of protein in cell nuclei were the same in all tissues of an organism. All that proteins had going for them was that they were known to be complex. Both Chargaff and Gulland had suggested that nucleic acids could vary by the sequence of the bases, perhaps providing a source of complexity. While still not excluding the possibility that proteins were involved, Mazia concluded: ‘DNA is the most likely candidate so far for the role of the material basis of heredity.’ 35
A couple of months earlier, in April 1950, Mazia had chaired a session at a special conference on the biochemistry of nucleic acids, held at the US Atomic Energy Commission’s Oak Ridge Laboratory in Tennessee. Among the speakers was Arthur Pollister, who with Mirsky had criticised Avery’s conclusions two years earlier. Pollister was changing his tune; he enthusiastically reported the data from Boivin’s laboratory that showed that the amount of DNA was constant in all diploid cells of a given species, before discussing the idea of a ‘DNA-gene’ and raising the possibility that the chemical structure of the gene was within reach. Nevertheless, Pollister was not completely convinced: the complexity of gene function led him to suggest that ‘important genic components other than DNA remain to be discovered.’ 36
Another speaker at the Oak Ridge meeting was Erwin Chargaff, who was acquiring some of the most telling evidence in favour of Avery’s conception of the role of DNA. Chargaff had been an early supporter of Avery’s hypothesis, and in 1950 he presented data on the precise base composition of nucleic acids, using paper chromatography to identify the bases by weight. He found that the proportion of the different bases was constant in all tissues of any species, but differed wildly between species. As Chargaff pointed out, these data disproved the tetranucleotide hypothesis, to the extent that anyone still thought it was true. 37 DNA was clearly not boring.
The
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