title: Mechanism of translational initiation in prokaryotes. Evidence for a direct effect of IF2 on the activity of the 30 S ribosomal subunit.
abstract: Initiation factor IF2 from either Escherichia coli or Bacillus stearothermophilus was found to possess the previously undetected property of stimulating the template-dependent ribosomal binding of aminoacyl-tRNAs with free alpha-NH2 groups. IF1, which had no detectable activity alone, was found to stimulate the activity of E. coli IF2 and, to a lesser extent, that of B. stearothermophilus IF2. Since in the absence of ribosomes not even a weak interaction between the two IF2 molecules and the aminoacyl-tRNAs was detected, the present findings indicate that IF2 can act at the ribosomal level stimulating aminoacyl-tRNA binding without prior formation of a binary complex with the aminoacyl-tRNA. IF2 does not appear to open or strengthen a weak A-site binding, but rather to enhance aminoacyl-tRNA binding to a 30 S site equivalent to the P-site by slowing down the rate of aminoacyl-tRNA dissociation from ribosomes.
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D015852:Eukaryotic Initiation Factor-2; D001411:Geobacillus stearothermophilus / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000494:pharmacology*; D011506:Proteins / Q000494:pharmacology*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl