An alternative to the RNA World Hypothesis

The RNA world hypothesis for the origin of life is widely accepted in spite of the complexity of RNA synthesis. An alternative hypothesis is advanced for the origin and evolution of protein and nucleic acid synthesis.  At an early stage synthesis of poly-(b-malic acid), the initial evolutionary predecessor of nucleic acids, and polypeptides was coupled.  This evolved into a singlet coding system in which glycine and alanine were specified by two derivatives of malic acid with different amide side chains.  In stages, the linear polyester backbone evolved into the phosphodiester backbone of RNA and the amide side chains evolved into the purine and pyrimidine bases.  The replication process for RNA used aminoacyl-NMP monomers (N= pyrimidine or purine) with a singlet coding system in which the four bases coded for glycine, alanine, valine and aspartic acid.  Ribosomal protein synthesis (RPS) evolved from coupled replication by using tRNAs and separating fidelity checking and peptide bond formation functions into small and large ribosomal subunits.  Continuity was maintained during the transition to the triplet process by using the same catalysts that aminoacylated NMPs to aminoacylate four different bases at the 3’ ends of the original tRNAs.  Four GNC codons used the central base to designate the same four amino acids that were coded in singlet replication.  Triplet-coded protein synthesis had the advantage of producing multiple copies of protein from a single copy of RNA, and eventually replaced protein synthesis via singlet-coded replication.  Evolution of the simple triplet-coded process into RPS is described.