An inhibitor of elongation factor G (EF-G) GTPase present in the ribosome wash of Escherichia coli: a complex of initiation factors IF1 and IF3?
An inhibitor of elongation factor G (EF-G) GTPase isolated from the ribosome wash of Escherichia coli was shown to stimulate the poly(A,U,G)- and initiation factor 2 (IF2)-dependent binding of N-formyl-[35S]Met-tRNAfMet to ribosomes. In the presence of saturating amounts of the EF-G GTPase inhibitor, neither addition of initiation factor 1 (IF1) nor addition of initiation factor 3 (IF3) caused a further stimulation of the formation of N-formyl-[35S]Met-tRNAfMET/poly(A,U,G)/ribosome complexes. Both IF1 and IF3 were shown to inhibit ribosome-dependent EF-G GTPase, especially when both initiation factors were added either in absence or in the presence of initiation factor 2 (IF2), poly(A,U,G) and N-formyl-Met-tRNAfMet. Therefore, we conclude that the EF-G GTPase inhibitor consisting of two polypeptide subunits with apparent molecular masses of 23,000 and 10,000 Da is a complex of initiation factors IF1 and IF3. The inhibition of EF-G GTPAse by IF3, but not the effects of IF1 in the presence or absence of IF3 could be reversed by increasing the Mg(2+)-concentration as already shown for the EF-G GTPase inhibitor. Therefore, IF1 as well as the EF-G GTPase inhibitor do not influence the ribosome-dependent EF-G GTPase by affecting the association of ribosomal subunits.
Nagel
K
K
Institut für Biochemie und Lebensmittelchemie, Universität Hamburg, Germany.
Voigt
J
J
D001426:Bacterial Proteins / Q000032:analysis*; D004926:Escherichia coli / Q000737:chemistry*; D015977:Eukaryotic Initiation Factor-1 / Q000032:analysis* / Q000502:physiology; D015852:Eukaryotic Initiation Factor-2 / Q000502:physiology; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000037:antagonists & inhibitors*; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors / Q000037:antagonists & inhibitors* / Q000502:physiology; D010448:Peptide Initiation Factors / Q000032:analysis* / Q000502:physiology; D011131:Polyribonucleotides / Q000378:metabolism; D039861:Prokaryotic Initiation Factor-1; D039665:Prokaryotic Initiation Factor-3; D012358:RNA, Transfer, Met / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D015977:Eukaryotic Initiation Factor-1; D015852:Eukaryotic Initiation Factor-2; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors; D010448:Peptide Initiation Factors; D011131:Polyribonucleotides; D039861:Prokaryotic Initiation Factor-1; D039665:Prokaryotic Initiation Factor-3; D012358:RNA, Transfer, Met; C008951:poly AUG; D020963:GTP Phosphohydrolase-Linked Elongation Factors