The genetic code, the transfer RNAs and the aminoacyl-tRNA-synthetases

Abstract

The first ideas on an intimate connection between RNA and protein synthesis go back to Brachet and Caspersson. We know now that their observations did not bear on the messenger RNA, but on ribosomal RNA. Nevertheless, it is thanks to them that this connection became familiar. Then Beadle formulated the hypothesis called the “one gene-one enzyme correlation”, but his ideas did never reach the formulation of a linear code relating genes and proteins. In 1950, Caldwell and Hinshelwood published a theory according to which nucleic acid, by a process similar to crystallization, ensures the order of the amino acids in the protein. Their ideas were rather confusing, since they were considering 23 amino acids and 5 units in the nucleic acids, namely the four bases and ribose phosphate. The authors were not mentioning whether their doublet code was overlapping or not. This article, only occasionally quoted exerted no influence on the later theories. On the other hand, a paper published by Dounce in 1952 was well read: it treats mainly of the possible chemical mechanisms of protein synthesis, but it suggests a code where each nucleotide codes for an amino acid, which automatically leads to an overlapping code. He did not realize that his code could be rejected by the mere inspection of the few known polypeptide sequences then available.