A molecular model for the origin of protein translation in an RNA world.
The RNA world hypothesis requires a ribozyme that was an RNA-directed RNA polymerase (ribopolymerase). A model for this, based on the core of the large subunit of the ribosome, is developed further. The geometry of a potential active site for this ribopolymerase suggests that it contained a cavity (now occupied by the aminoacyl-tRNA) and that an amino acid binding in this might have "poisoned" the ribopolymerase by cross-reacting with the nucleoside triphosphate before polymerization could occur. Based on a similarity to the active site components of the class-I tRNA synthetase enzymes it is proposed that the amino acid could become attached to the nascent RNA transcript producing a variety of amino-acylated tRNA-like products. Using base-pairing interactions, it is suggested that some of these molecules might cross-link two ribopolymerases giving rise to a precursor of the modern ribosome with two subunits linked by tRNA. A hybrid dimer, half polymerase and half proto-ribosome, could account for mRNA translocation before the advent of protein elongation factors. Some implications for the genetic code are discussed.
Taylor
William R
WR
Division of Mathematical Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK. wtaylor@nimr.mrc.ac.uk <wtaylor@nimr.mrc.ac.uk>
D000818:Animals; D005815:Genetic Code; D008958:Models, Molecular; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics*; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism; D014178:Translocation, Genetic
D012333:RNA, Messenger; D012343:RNA, Transfer; D012324:RNA-Dependent RNA Polymerase