"The origin of the genetic code"

Date:
1967
Reference:
PP/CRI/H/4/9
Catalogue details

Licence: In copyright

Credit: "The origin of the genetic code". Source: Wellcome Collection.

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    The Origin of the Genetic Code F. H. C. Crick Medical Research Council Laboratory of Molecular Biology Hills Road, Cambridge, England (.Received 21 August 1968) The general features of the genetic code are described. It is considered that originally only a few amino acids were coded, but that most of the possible codons were fairly soon brought into use. In subsequent steps additional amino acids were substituted when they were able to confer a selective advantage, until even tually the code became frozen in its present form. Introduction The substance of this paper was originally presented at a meeting of the British Biophysical Society in London on 20 December 1966. A very brief account appeared shortly after in a letter to Nature (Crick, 1967a). When this manuscript was in its first draft, Dr Leslie Orgel told me that he had already prepared a draft of a paper on a related theme. We therefore decided to publish our two papers together and have collated them to some extent to avoid overlap. We have not done tills for all passages in the two papers which touch on the same topic, preferring on occasions to let our slightly different points of view be expressed as differences in treatment and emphasis. However, broadly speaking, each of us agrees with the opinion expressed by the other. Since this paper was originally drafted a very full discussion has appeared in Woese's book The Genetic Code, which should be consulted for a fuller discussion of many of the points touched on here. The Structure of the Present Genetic Code The structure of the genetic code is now fairly well known. The code is a non- overlapping triplet code. Most, but not all, of the 64 triplets stand for one or another of the 20 amino acids and, in most cases, each amino acid is represented by more » than one codon. The best present version of the code is shown in Table 1. This is taken from the 1966 Cold Spring Harbor Symposium on The Genetic Code, to which the reader is referred as a source of references for many of the topics discussed here. 4 Before starting on a detailed examination of this Table a few words of caution are # necessary Although the code shown there has been mainly derived from studies on . Escherichia coli, it must be very similar in such widely different organisms as tobacco 1? plants and man. In what follows I shall assume, for convenience of exposition, that |fit is identical in all organisms, which is very far from being proved. In fact, it is J probably untrue for the starting codons, i 367