title: Mechanism of ribosomal translocation. tRNA binds transiently to an exit site before leaving the ribosome during translocation.
abstract: Escherichia coli ribosomes have a site (E) to which deacylated tRNA binds transiently before leaving the ribosome during translocation. The affinity of the site is Mg2+ dependent and low at physiological Mg2+ concentrations. Correct codon-anticodon interaction is unnecessary in this site. With these features, the E site cannot reduce frameshift errors through additional mRNA anchorage. Occupancy of the A site does not influence the tRNA binding in the E site, although a conformational change of elongation factor G, brought about by GTP hydrolysis, is necessary for efficient tRNA release. The tRNA can dissociate unhindered from the E site when the elongation factor is bound to the ribosome by fusidic acid. During elongation, the thermodynamically stable state is not attained, since E site occupation inhibits translocation. However, the E site can aid elongation by providing an intermediate state for tRNA dissociation, dispersing the process into more than one step.
authors.affiliation: Institute für Physiologische Chemie, Universität München, F.R.G.
authors.forename: J M
authors.initials: JM
authors.lastname: Robertson
authors.forename: W
authors.initials: W
authors.lastname: Wintermeyer
mesh_terms: D000495:Allosteric Site; D001665:Binding Sites; D003062:Codon; D004926:Escherichia coli / Q000235:genetics; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors / Q000378:metabolism; D010652:Phenylalanine-tRNA Ligase / Q000378:metabolism; D014176:Protein Biosynthesis; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D013696:Temperature; D014756:Viomycin / Q000494:pharmacology
chemical_list: D003062:Codon; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors; D012346:RNA, Transfer, Amino Acyl; D006160:Guanosine Triphosphate; D010652:Phenylalanine-tRNA Ligase; D008274:Magnesium; D014756:Viomycin