General Nature of the Genetic Code for Proteins

HERE is now a mass of indirect evidence which suggests that ths amino-a&d sequence along the polypeptids chain of a protein is determined by the sequence of the bases along some particular part of the nucleic acid of the genetic material. Since there are twenty common amino-acids found throughout Sature, but only four common bases, it haa often been surmised that the sequence of the four baaes is in soms way a code for the sequence of the aminoacids. In this article ws report genetic experiments which, togsther with the work of others, suggest that the genetic code is of the foUowing general type: (a) A group of three bases (or, leas likely, a multiple of three bases) codes one amino-acid. (b) The code is not of the overlapping type (see Fig. 1). (c) The sequence of the baass is read from a fixed Btarting point. This dstsrminsa how the long sequences of bases are to bs correctly read off as triplets. There ars no special ‘commas’ to show how to select the right triplets. If the starting point is displaced by one bass, then the reading into triplets is displaced, and thus becomes incorrsct. (d) The code is probably ‘degenerate’; that is, in general, one particular ammo-acid can be coded by one of several tripieta of bases.