Studies on the mechanism of action of a eukaryotic codon-dependent factor specific for initiator Met-tRNAf and ribosomal 40 S subunits.
A putative eukaryotic initiation factor purified from rat liver cytosol promotes the ApUpGp- and Mg2+-dependent, GTP-independent binding of initiator Met-tRNAf to ribosomal 40 S subunits. The isotopically-labeled factor binds specifically to 40 S subunits to form a binary complex which can then bind Met-tRNAf in the presence of ApUpGp. When 60 S subunits are added, an 80 S complex is formed which contains Met-tRNAf but not the factor. The Met-tRNAf bound to 80 S ribosomes reacts quantitatively with puromycin. Purified 40 S subunits exist in the form of monomers and dimers. The factor converts monomers, which appear to contain one molecule of tRNA, to a form that does not contain tRNA and dimerizes readily. Deacylated tRNA inhibits dimerization and, in the presence of the factor, converts dimers to the monomeric form; thus, the factor appears to act in a reversible manner. This protein factor may play a role in the removal of tRNA from 40 S subunits, which could be generated as a consequence of chain termination, a prerequisite to the bindig of Met-tRNAf.
D000818:Animals; D003062:Codon / Q000235:genetics*; D003600:Cytosol / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics*; D012346:RNA, Transfer, Amino Acyl / Q000235:genetics*; D012358:RNA, Transfer, Met; D051381:Rats; D012270:Ribosomes / Q000378:metabolism*
D003062:Codon; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; C024988:tRNA, formylmethionine-