title: Is the three-site model for the ribosomal elongation cycle sound?
abstract: The release of deacylated tRNA from the ribosome as a result of translocation has been studied. Translating ribosomes prepared with poly(U)-S-S-Sepharose columns have been used. It has been shown that deacylated tRNA released from the ribosomal P site as a result of translocation rebinds with the vacated A site. Consistent with the known properties of the A site of the ribosome, this interaction is reversible, Mg2+-dependent, codon-specific and is inhibited by the antibiotic tetracycline. It has been concluded that the proposed three-site model of the ribosomal elongation cycle (Rheinberger and Nierhaus (1983) Proc. Natl. Acad. Sci. USA 80, 4213-4217) is not sound: the experimentally observed 'retention' of the deacylated tRNA on the ribosome after translocation can be explained by a codon-dependent rebinding to the A site, rather than by its transition to the 'E site', i.e., in terms of the classical two-site model.
mesh_terms: D008954:Models, Biological; D010441:Peptide Chain Elongation, Translational; D014176:Protein Biosynthesis; D012360:RNA, Transfer, Phe / Q000235:genetics; D012270:Ribosomes / Q000502:physiology*; D014178:Translocation, Genetic
chemical_list: D012360:RNA, Transfer, Phe