9 The Roles of RNA in the Synthesis of Protein

Abstract

In december, 1962, james watson delivered a Nobel Prize lecture in Stockholm entitled “Involvement of RNA in the Synthesis of Protein” (Watson 1963) in which he described what was then known about protein synthesis, and how it had come to be known. When one reads the text of his lecture today, one is struck by how much had already been learned about protein synthesis by then; the picture Watson painted for his audience that day was correct in its essence. However, there were still lots of missing pieces. For example, in 1962, no one knew how many tRNA-binding sites were on the ribosome, nor was it clear whether the ribosomes in a cell all have the same chemical composition. Neither the three-dimensional structures nor the sequences were known for any of the macromolecules involved in protein synthesis, and nothing was understood about their mechanisms of action.

In 1962, only three kinds of RNA were known: transfer RNAs, which were then called soluble RNAs; messenger RNAs, which had been discovered only recently; and ribosomal RNAs. It was understood that mRNAs convey sequence information from the genome to the protein synthetic apparatus, and that tRNAs are carrier molecules for amino acids that perform two functions. First, esterification of amino acids to tRNAs, which is driven by ATP hydrolysis, activates them; the formation of polypeptides from aminoacyl-tRNAs is spontaneous under intracellular conditions, but the formation of polypeptides from free amino acids is not. Second, tRNAs are adapter molecules. At least one tRNA is...