Regulation of elongation factor G GTPase activity by the ribosomal state. The effects of initiation factors and differentially bound tRNA, aminoacyl-tRNA, and peptidyl-tRNA.
The elongation factor G (EF-G) is responsible for the translocation of the ribosome along the mRNA chain. Under in vitro conditions, EF-G exhibits a very active uncoupled GTPase activity which is dependent on the presence of ribosomes and is modulated by mRNA-dependent binding of tRNA. In the absence of tRNA, uncoupled EF-G GTPase is inhibited by initiation factors IF1 and IF3, but not by initiation factor IF2. In the presence of N-fMet-tRNAfMet and poly(A,U,G) or in the presence of N-acetyl-Phe-tRNAPhe and poly(U), initiation factor IF2 causes an additional decrease of the uncoupled EF-G GTPase activity. This effect, however, is dependent on the presence of IF1 and IF3 and is obviously due to the mRNA- and initiation factor-dependent binding of N-fMet-tRNAfMet and N-acetyl-Phe-tRNAPhe, respectively, to the ribosomal P-site. Non-enzymatic binding of N-fMet-tRNAfMet and N-acetyl-Phe-tRNAPhe, however, causes a stimulation of uncoupled EF-G GTPase activity. The same effects are observed for Met-tRNA, Phe-tRNAPhe and uncharged tRNA. These findings are discussed in the light of the three-site model of the ribosome and the mechanism of translocation.
Voigt
J
J
Botanisches Institut, Technischen Universität Braunschweig, Germany.
Nagel
K
K
D002848:Chromatography, DEAE-Cellulose; D004926:Escherichia coli / Q000378:metabolism*; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism*; D015636:Magnesium Chloride / Q000494:pharmacology; D008954:Models, Biological; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010448:Peptide Initiation Factors / Q000302:isolation & purification / Q000378:metabolism*; D011072:Poly U / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D012358:RNA, Transfer, Met; D012360:RNA, Transfer, Phe / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors; D010448:Peptide Initiation Factors; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; D012360:RNA, Transfer, Phe; C024988:tRNA, formylmethionine-; C019037:tRNA, peptidyl-; D015636:Magnesium Chloride; D011072:Poly U; D020963:GTP Phosphohydrolase-Linked Elongation Factors