title: The elongation factor Tu from Escherichia coli, aminoacyl-tRNA, and guanosine tetraphosphate form a ternary complex which is bound by programmed ribosomes.
abstract: The interaction of the Escherichia coli elongation factor Tu guanosine tetraphosphate complex (EF-Tu ppGpp) with aminoacyl-tRNAs(aa-tRNA) was reinvestigated by gel filtration and hydrolysis protection experiments. These experiments show that EF-Tu X ppGpp like EF-Tu X GDP (Pingoud, A., Block, W., Wittinghofer, A., Wolf, H. & Fischer, E. (1982) J. Biol. Chem. 257, 11261-11267) forms a fairly stable complex with Phe-tRNAPhe, KAss being 0.6 X 10(5) M-1 at 25 degrees C. The binding of the EF-Tu X ppGpp X aa-tRNA complex to programmed ribosomes was investigated by a centrifugation technique. It is shown that this complex is bound codon-specific with KAss = 3 X 10(7) M-1 at 0 degrees C and that it stimulates peptidyl transfer. A numerical estimation of the intracellular concentration of EF-Tu X GTP X aa-tRNA and EF-Tu X ppGpp X aa-tRNA during normal growth and under the stringent response indicates that ppGpp accumulation does affect the EF-Tu X GTP X aa-tRNA concentration but does not lead to major depletion of this pool. Furthermore, due to the higher affinity of EF-Tu X GTP to aa-tRNA and of the ternary complex EF-Tu X GTP X aa-tRNA to the ribosome, EF-Tu X ppGpp X aa-tRNA binding to the ribosome is not significant. According to our measurements and calculations, therefore, a direct participation of EF-Tu in slowing down the rate of protein biosynthesis and improving its accuracy during amino acid starvation is not obvious.
mesh_terms: D004926:Escherichia coli; D006159:Guanosine Tetraphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D046911:Macromolecular Substances; D010444:Peptide Elongation Factor Tu; D010445:Peptide Elongation Factors / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D010445:Peptide Elongation Factors; D012346:RNA, Transfer, Amino Acyl; D006159:Guanosine Tetraphosphate; D006160:Guanosine Triphosphate; D010444:Peptide Elongation Factor Tu