title: Were RNA replication and translation directly coupled in the RNA (+protein?) World?
abstract: The ribosome is proposed to have evolved from an ancestor that simultaneously replicated and translated template RNA. At its decoding site, this ancestor to the ribosome carried a ribozyme that assembled product RNA by sequentially ligating anticodon triplets excised from tRNAs. This ribozyme was the ancestor of the Group I introns, which are still present on some ribosomal RNA precursors. Coupling of reversible RNA replication by transesterification with the thermodynamically favourable process of transpeptidation provides a rationale for the evolution of the complete ribosome as a replicase for large RNAs in the RNA (+protein?) world. A detailed and experimentally verifiable mechanism can be proposed for simultaneous replication and translation. Sequence requirements for recognition of the decoding complex as a substrate helix by these ribozymes are consistent with earlier models for the origin of the genetic code, but require an indirect mode for ribosomal self-replication. This proposal has the potential to explain the location of Group I introns in the anticodon loops of some tRNAs.
authors.affiliation: CSIRO Division of Entomology, Canberra, Australia.
authors.forename: K H
authors.initials: KH
authors.lastname: Gordon
mesh_terms: D000818:Animals; D005075:Biological Evolution; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics*; D012270:Ribosomes / Q000235:genetics*
chemical_list: D011506:Proteins; D012335:RNA, Ribosomal