title: Role of yeast elongation factor 3 in the elongation cycle.
abstract: Investigation of the role of the polypeptide chain elongation factor 3 (EF-3) of yeast indicates that EF-3 participates in the elongation cycle by stimulating the function of EF-1 alpha in binding aminoacyl-tRNA (aa-tRNA) to the ribosome. In the yeast system, the binding of the ternary complex of EF-1 alpha.GTP.aa-tRNA to the ribosome is stoichiometric to the amount of EF-1 alpha. In the presence of EF-3, EF-1 alpha functions catalytically in the above mentioned reaction. The EF-3 effect is manifest in the presence of ATP, GTP, or ITP. A nonhydrolyzable analog of ATP does not replace ATP in this reaction, indicating a role of ATP hydrolysis in EF-3 function. The stimulatory effect of EF-3 is, in many respects, distinct from that of EF-1 beta. Factor 3 does not stimulate the formation of a binary complex between EF-1 alpha and GTP, nor does it stimulate the exchange of EF-1 alpha-bound GDP with free GTP. The formation of a ternary complex between EF-1 alpha.GTP.aa-tRNA is also not affected by EF-3. It appears that the only reaction of the elongation cycle that is stimulated by EF-3 is EF-1 alpha-dependent binding of aa-tRNA to the ribosome. Purified elongation factor 3, isolated from a temperature-sensitive mutant, failed to stimulate this reaction after exposure to a nonpermissive temperature. A heterologous combination of ribosomal subunits from yeast and wheat germ manifest the requirement for EF-3, dependent upon the source of the "40 S" ribosomal subunit. A combination of 40 S subunits from yeast and "60 S" from wheat germ showed the stimulatory effect of EF-3 in polyphenylalanine synthesis (Chakraburtty, K., and Kamath, A. (1988) Int. J. Biochem. 20, 581-590). However, we failed to demonstrate the effect of EF-3 in binding aa-tRNA to such a heterologous combination of the ribosomal subunits.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee 53226.
authors.forename: A
authors.initials: A
authors.lastname: Kamath
authors.forename: K
authors.initials: K
authors.lastname: Chakraburtty
mesh_terms: D005656:Fungal Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D009154:Mutation; D010441:Peptide Chain Elongation, Translational; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012360:RNA, Transfer, Phe / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D005656:Fungal Proteins; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors; D012346:RNA, Transfer, Amino Acyl; D012360:RNA, Transfer, Phe; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins; C111584:YEF3 protein, S cerevisiae; D006160:Guanosine Triphosphate