title: Reverse translocation of tRNA in the ribosome.
abstract: A widely held view is that directional movement of tRNA in the ribosome is determined by an intrinsic mechanism and driven thermodynamically by transpeptidation. Here, we show that, in certain ribosomal complexes, the pretranslocation (PRE) state is thermodynamically favored over the posttranslocation (POST) state. Spontaneous and efficient conversion from the POST to PRE state is observed when EF-G is depleted from ribosomes in the POST state or when tRNA is added to the E site of ribosomes containing P-site tRNA. In the latter assay, the rate of tRNA movement is increased by streptomycin and neomycin, decreased by tetracycline, and not affected by the acylation state of the tRNA. In one case, we provide evidence that complex conversion occurs by reverse translocation (i.e., direct movement of the tRNAs from the E and P sites to the P and A sites, respectively). These findings have important implications for the energetics of translocation.
authors.affiliation: Department of Microbiology, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Shoji
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Walker
authors.forename: Kurt
authors.initials: K
authors.lastname: Fredrick
mesh_terms: D000215:Acylation; D001483:Base Sequence; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008969:Molecular Sequence Data; D009355:Neomycin / Q000494:pharmacology; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012329:RNA, Bacterial / Q000235:genetics*; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D013307:Streptomycin / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology; D014178:Translocation, Genetic
chemical_list: D010445:Peptide Elongation Factors; D011500:Protein Synthesis Inhibitors; D012329:RNA, Bacterial; D006160:Guanosine Triphosphate; D012343:RNA, Transfer; D013752:Tetracycline; D009355:Neomycin; D013307:Streptomycin