Open AccessCooperative Effects of Initiation Factors and fMet‐Trna in the Formation of the 40‐S Initiation Complex
Author(s) -
HOFSTAD Gerard A. J. M.,
FOEKENS John A.,
ELSEN Peter J.,
VOORMA Harry O.
Publication year - 1976
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1976.tb10438.x
Subject(s) - gtp' , transfer rna , protein subunit , chemistry , initiation factor , biophysics , biology , biochemistry , binding site , microbiology and biotechnology , stereochemistry , rna , enzyme , ribosome , gene
In this paper the mode of action of IF‐1 in 40‐S initiation complex formation was studied with MS 2 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 K m 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.