"On loopy codes"

Date:
[c. 1961]
Reference:
PP/CRI/H/3/2
Catalogue details

Licence: In copyright

Credit: "On loopy codes". Source: Wellcome Collection.

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    * On Loopy Godes The basic dilemma in the coding problem is that the base-composition of the DM of different bacterial species varies over a wide range, while the proteins produced by these cells seem, in amino acid composition, to be rather similar. This has been discussed in detail elsewhere (Crick, 1959)• Recent developments suggest that we can push the dilemma one step further. It now seems likely that the genetic information which determines the amino acid sequences of proteins, and which is presumed to be contained in the base- sequence of the genetic DNA, is not passed on to ribosomal RNA but to a quite different species of RNA known as messenger SNA (Brenner, Jacob, and Meselson, I96I). The fragmentary evidence available suggests that the base-composition of this RNA is similar to that of DNA from which it is copied (Volkin and Astrachan (1956), Astrachan and Yolkin (1958) Yeas and Vincent (1958) and Astrachan, personal communication). In spite of this evidence there is a strong temptation to believe that the code is the same throughout Nature. How can this be so if the base composition of the messenger RNA is greatly different in organisms where proteins have a similar overall composition? In this short note we wish to point out several rather simple ways in which this might come about if we suppose that messenger RNA has a structure involving loops. In each of the codes the magic number 20 appears in a rather natural way. It has been deduced by Fresco and Alberts (i960), from studies of synthetic polyribonucleotides in solution, that where a base-pair which does not match occurs in an RNA double helix the extra residue (or residues) is looped out of the structure. Fresco,