title: A proposed role for IF-3 and EF-T in maintaining the specificity of prokaryotic initiation complex formation.
abstract: Initiation factor-free 30S subunits of E. coli ribosomes bind aminoacyl-tRNAs more efficiently than fMet-tRNA(fMet). Elongator-tRNA binding was unaffected by IF-1 or IF-2 but was inhibited by IF-3. Their combination reduced this binding up to 40% and stimulated that of fMet-tRNA(fMet). Unexpectedly, EF-T also prevented elongator-tRNA binding by complexing both to the 30S and to the aminoacyl-tRNAs. Using AUGU3 as mRNA, elongator-tRNAs competed with fMet-fRNA(fMet) and with tRNA(fMet), fMet-tRNA(fMet) reacted with puromycin after addition of 50S subunits suggesting that it occupied the P site. EF-T directed binding of phe-tRNA to the 30S.AUGU3 complex at the A site only if fMet-tRNA(fMet) or tRNA(fMet) filled the P/E site. We propose that one function of EF-T may be to prevent the entry of aminoacyl-tRNAs into the 30S particle during initiation. The possibility that a special site for fMet-tRNA resides on 16S rRNA is also discussed.
authors.affiliation: Banting and Best Department of Medical Research, University of Toronto, Ontario Canada.
authors.forename: M C
authors.initials: MC
authors.lastname: Ganoza
authors.forename: C
authors.initials: C
authors.lastname: Cunningham
authors.forename: D G
authors.initials: DG
authors.lastname: Chung
authors.forename: T
authors.initials: T
authors.lastname: Neilson
mesh_terms: D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive; D004926:Escherichia coli; D010441:Peptide Chain Elongation, Translational; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D010445:Peptide Elongation Factors / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology*; D010448:Peptide Initiation Factors / Q000502:physiology*; D039665:Prokaryotic Initiation Factor-3; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012356:RNA, Transfer, Leu / Q000378:metabolism; D012360:RNA, Transfer, Phe / Q000378:metabolism; D012362:RNA, Transfer, Ser / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism
chemical_list: D010445:Peptide Elongation Factors; D010448:Peptide Initiation Factors; D039665:Prokaryotic Initiation Factor-3; D012346:RNA, Transfer, Amino Acyl; D012356:RNA, Transfer, Leu; D012360:RNA, Transfer, Phe; D012362:RNA, Transfer, Ser; C036506:elongation factor T