title: Kinetic basis for global loss of fidelity arising from mismatches in the P-site codon:anticodon helix.
abstract: Faithful decoding of the genetic information by the ribosome relies on kinetically driven mechanisms that promote selection of cognate substrates during elongation. Recently, we have shown that in addition to these kinetically driven mechanisms, the ribosome possesses a post peptidyl transfer quality control system that retrospectively monitors the codon-anticodon interaction in the P site, triggering substantial losses in the specificity of the A site during subsequent tRNA and RF selection when a mistake has occurred. Here, we report a detailed kinetic analysis of tRNA selection in the context of a mismatched P-site codon:anticodon interaction. We observe pleiotropic effects of a P-site mismatch on tRNA selection, such that near-cognate tRNA is processed by the ribosome almost as efficiently as cognate. In particular, after a miscoding event, near-cognate codon-anticodon complexes are stabilized on the ribosome to an extent similar to that observed for cognate ones. Moreover, the two observed forward rates of GTPase activation and accommodation are greatly accelerated (∼10-fold) for near-cognate tRNAs. Because the ensemble of effects of a mismatched P site on substrate selection were found to be different from those reported for other ribosomal perturbations and miscoding agents, we propose that the structural integrity of the mRNA-tRNA helix in the P site provides a distinct molecular switch that dictates the specificity of the A site.
authors: Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors: Hani S
authors: HS
authors: Zaher
authors: Rachel
authors: R
authors: Green
mesh_terms: D000926:Anticodon / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020137:Base Pair Mismatch; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003062:Codon / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D009690:Nucleic Acid Conformation; D010441:Peptide Chain Elongation, Translational; D010444:Peptide Elongation Factor Tu / Q000378:metabolism; D010454:Peptide Termination Factors / Q000378:metabolism; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012331:RNA, Fungal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism
chemical_list: D000926:Anticodon; D003062:Codon; D010454:Peptide Termination Factors; D012329:RNA, Bacterial; D012331:RNA, Fungal; D020558:GTP Phosphohydrolases; D010444:Peptide Elongation Factor Tu