A GTPASE REACTION ACCOMPANYING THE REJECTION OF LEU-TRANSFER RNA2 BY UUU-PROGRAMMED RIBOSOMES - PROOFREADING OF THE CODON-ANTICODON INTERACTION BY RIBOSOMES

  • 1 January 1981
    • journal article
    • research article
    • Vol. 256  (1) , 81-86
Abstract
The characteristics of a GTPase reaction between poly(U)-programmed ribosomes, EFTu.cntdot.GTP, and the near-cognate aminoacyl (aa)-tRNA, Leu-tRNA2Leu [from Escherichia coli], were 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.cntdot.GTP in its substrate requirements, in its involving EFTu.cntdot.GTP.cntdot.aa-tRNA ternary complexes, and in its requiring a free ribosomal A-site. The non-cognate 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-tRNA2Leu 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.