title: Effect of initiation factor 3 binding on the 30S ribosomal subunits of Escherichia coli.
abstract: Under certain conditions, initiation factor 3 (IF-3) can cause the release of aminoacyl-tRNA bound to 30S ribosomal subunits of E. coli. It is shown that this IF-3-induced aminoacyl-tRNA release cannot be attributed to either nucleolytic attack or competition between IF-3 and aminoacyl-tRNA for the same ribosomal binding site. It was found that the 30S-aminoacyl-tRNA-codon complexes formed in the absence of IF-3 are intrinsically different from those prepared in the presence of IF-3. In the absence of IF-3, the ribosomal binding of aminoacyl-tRNA is a virtually irreversible process, since the bound aminoacyl-tRNA can neither be spontaneously released upon dilution nor exchanged for unbound aminoacyl-tRNA. In the presence of IF-3, the binding of one molecule of IF-3 per 30S ribosome renders the binding of aminoacyl-tRNA reversible upon dilution and promotes exchange between bound and unbound aminoacyl-tRNA. It is suggested that this difference is due to a conformational transition of the 30S ribosomal subunit induced by the binding of IF-3. The possible implications of this finding in relation to the mechanism of action of IF-3 and its functional role in the cell are discussed.
mesh_terms: D001665:Binding Sites; D002250:Carbon Radioisotopes; D004926:Escherichia coli / Q000378:metabolism*; D010448:Peptide Initiation Factors; D010649:Phenylalanine; D012329:RNA, Bacterial / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D013696:Temperature
chemical_list: D002250:Carbon Radioisotopes; D010448:Peptide Initiation Factors; D012329:RNA, Bacterial; D010649:Phenylalanine; D012343:RNA, Transfer