[Untitled draft]

Date:
[1953]
Reference:
PP/CRI/H/1/12/4
Catalogue details

Licence: In copyright

Credit: [Untitled draft]. Source: Wellcome Collection.

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    formed. We now postulate that the polymerisation of the monomers to form a new chain is only possible if the resulting chain can form the proposed structure . This is plausible because stefric reasons would not allow nucleotides crystallised onto the first chain to approach one another in such a way that they could be joined together into a new chain, unless they were those nucleotides which were necessary to form our structure. Whether a special enzyme ins required to carry out the polymerisation, or whether the single helical chain coacf ör already formed act^ effectively as an enzyme remains to be seen. I Our structure, as described', is an open one. There is room between the pair of polynucleotide chains for a polypeptide chain to wind round the same helical axis. It may be significant that the distance between adjacent phosphorus atoms, 7.1 $, is close to the repeat of a fully extended polypeptide chain. We think it probable that in the sperm head, and in artificial nucleoproteins, the polypep tide chain occupies this position. The relative weakness of the second layer-line in the published X-ray pictures^'® is crudely compat ible with such an idea. The function of the protein might well be to control the coiling and uncoiling, to assist in holding a single polynucleotide chain in a helical configuration, or some other non-specific, or quasi-specific function. «cA«A £4,^ It seems plausible to us that a spontaneous mutation, ttesrt te be is, a change in the sequence of bases, may be due to a base occuring very occasionally in one of the less likely tautomeric forms, at that moment when the complementary chain is being formed. While adenine will normally pair with thymine, if there is a tautomeric shift of one of its hydrogen atoms it can pair with cytosine. The next time