Figure 1. A poly-tRNA model for early peptide-synthesis and the emergence of a trrnD-type primitive mRNA (trrnD-mRNA) from tRNAGly. The model (B) shows how primitive tRNAGly could have converted to be an earliest mRNA ( trrnD-mRNA ) by interacting with the 16 (presumptive) anticodons of the tRNA-replicator riboorganisms. poly-tRNA = poly-tRNA region of the RNA transcript from the B. subtilis trrnD operon shown in (A) ; trrnD-peptide = a hypothetical 16-amino acid (aa)-peptide whose aa sequence is in the same order of the 16 aa specificities in the 16 tRNAs of this operon. ; tRNAGly = tRNAGly gene in the trrnD-operon. ; D-3-phosphoglycerate transporter protein B = pgtB protein encoded by the pgtB gene in Salmonella typhymurium. ; Gly-RS = glycyl-tRNA synthetase alpha subunit encoded by the glyS gene in E. coli.