An evolutionary theory based on a protein-mRNA co-synthesis hypothesis
A new hypothesis is proposed, that early life possessed a mechanism for the simultaneous synthesis of a polypeptide and its coding mRNA. Early tRNAs and mRNAs are considered to have been pairs of simple complementary nucleotide triplets, able to catalyze peptide bond formation and joining of the codon triplets. An in silico build stereochemical model for such a process is presented. A model for the evolution of modern tRNAs and ribosomal translation from such a primitive apparatus is also presented. Modern tRNAs are viewed as consisting of two halves, one of which evolved from ancient elongating mRNA and the other from a primitive also elongating tRNA. The probable origin of the ACC triplet at the amino-acid-accepting arm of the tRNAs is discussed. A theoretical scheme for the generation of mutations in response to the presence of chemical or physical factors and to their effect on newly synthesized polypeptides, based on the polypeptide-mRNA co-synthesis hypothesis, is presented. Messenger RNA nicking during each step of peptide bond formation and trans-translation of a different mRNA or codon triplet, in response to ribosome stalling, are the essential elements of the proposed theory for directed mutability.