title: Cooperative effects of initiation factors and fMet-tRNA in the formation of the 40-S initiation complex.
abstract: In this paper the mode of action of IF-1 in 40-S initiation complex formation was studied with MS2 RNA as messenger. Using initiation factors IF-2 and IF-3 labeled in vitro it appeared that IF-1 did not influence the binding of these factors in the absence of fMet-tRNA. However, in the presence of fMet-tRNA it was found that the enhancement of the fMet-tRNA binding by IF-1 was accompanied with an equimolar increase in binding of IF-2. Moreover, it appeared that also in absence of IF-1, fMet-tRNA binding is coupled with an equimolar enhancement of the IF-2 binding, which suggests the existence of a preribosomal complex between IF-2 and fMet-tRNA. The apparent Km values for both the binding of fMet-tRNA and IF-2 to 30-S subunits were determined and appeared to be equal, which makes a functioning of such a preribosomal complex in protein initiation very likely. The participation of GTP in this complex will be discussed. Functions of IF-1 in dissociation and recycling of IF-2, described by others, and the stimulation on the 30-S subunit level might well be explained as pleiotropic effects of one basic action of IF-1, i.e. a conformational change of 30-S subunits.
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D003090:Coliphages / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D008715:Methionine; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors; D011485:Protein Binding; D012343:RNA, Transfer / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
chemical_list: D010448:Peptide Initiation Factors; D012367:RNA, Viral; D012343:RNA, Transfer; D008715:Methionine