title: A GTPase reaction accompanying the rejection of Leu-tRNA2 by UUU-programmed ribosomes. Proofreading of the codon-anticodon interaction by ribosomes.
abstract: The characteristics of a GTPase reaction between poly(U)-programmed ribosomes, EFTu . GTP, and the near-cognate aminoacyl (aa)-tRNA, Leu-tRNA Leu 2, have been studied to assess the role of this reaction in proofreading of the codon-anticodon interaction. The reaction resembles the GTPase reaction with cognate aa-tRNAs and EFTu . GTP in its substrate requirements, in its involving EFTu . GTP . aa-tRNA ternary complexes, and in its requiring a free ribosomal A-site. The noncognate reaction differs from the cognate one in that aa-tRNA becomes stably bound to the ribosomes only 5% of the time; it therefore seems best characterized as an abortive enzymatic binding reaction. The rate of reaction is a significant fraction (4%) of that of the cognate aa-tRNA, indicating that recognition of ternary complexes by ribosomes involves a level of error greater than that of translation as a whole. The rejection of the noncognate aa-tRNA following GTP hydrolysis is therefore a vital step in the translation process and fulfills the criteria set for a proofreading reaction. Leu-tRNA Leu 2 which escapes rejection through proofreading, forms a stable complex with the ribosomal A-site, so it appears that the Leu-tRNA2 which was rejected never reached the A-site and that proofreading precedes full A-site binding.
mesh_terms: D000926:Anticodon / Q000378:metabolism*; D003062:Codon / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D007700:Kinetics; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011072:Poly U / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D000926:Anticodon; D003062:Codon; D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; D011072:Poly U; D012343:RNA, Transfer; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases