Polynucleotide replication coupled to protein synthesis: a possible mechanism for the origin of life.

A mechanism is suggested for the replication under primitive conditions of long polynucleotides by the sequential incorporation of sequences related to those of modern transfer RNAs. It is proposed that replication of such molecules became established as the result of a replicative advantage arising from the concomitant linkage together of amino acids to form polypeptides. Initially these polypeptides may have been of random sequence. Selection of primitive tRNAs in which the amino acid and anticodon stem sequences were rotationally symmetrical could have led to specific, anticodon-directed aminoacylation and fixation of the genetic code along the lines suggested by Hopfield. (Hopfield, 1978). The primitive replication-coupled system would then have been able to synthesize specific proteins containing one amino acid residue for each primitive tRNA incorporated during replication. The end result of this line of evolution is postulated to have been a nucleoprotein structure resembling the ribosome. The primitive system would then have been able to give rise directly to triplet-coded protein synthesis. Some recent RNA sequence data are discussed which are consistent with derivation of modern protein synthesis from the primitive replication-coupled mechanism.