guanosine-tetraphosphate and methylglucoside

Guanosine 3',5'-bispyrophosphate (ppGpp) accumulates in bacteria in response to either amino acid or energy source starvation. Here we demonstrate that levels of ppGpp similar to those induced by amino acid starvation inhibit the rate of protein synthesis by 84-91%. The intracellular concentration of ppGpp is manipulated in our studies by increasing the expression of a truncated relA gene encoding a smaller but catalytically active peptide with ppGpp synthetase activity. We find that the intracellular activity of the truncated RelA peptide is insensitive to chloramphenicol, unlike the product of the wild-type relA gene, ppGpp synthetase I. Previously, this same ppGpp expression system was used (Schreiber, G., Metzger, S., Aizenman, E., Roza, S., Cashel, M., and Glaser, G. (1991) J. Biol. Chem. 226, 3760-3767) to demonstrate that increasing the ppGpp concentration inhibits growth and ribosomal RNA transcription, and they found suggestive evidence for ppGpp inhibition of protein synthesis. We further investigated the effect of ppGpp on protein synthesis and find that ppGpp is a potent inhibitor of protein synthesis as well as glycerol accumulation but has no effect on transport of methionine, the amino acid used in measuring protein synthesis rates, or on uptake of alpha-methylglucoside, a non-metabolizable analogue of glucose.

Topics: Biological Transport; Chloramphenicol; Escherichia coli; Glycerol; GTP Pyrophosphokinase; Guanosine Tetraphosphate; Ligases; Methionine; Methylglucosides; Protein Biosynthesis; Protein Synthesis Inhibitors

The accumulation of RNA and protein and the kinetics of nucleoside triphosphate and guanosine polyphosphate pools during amino acid starvation and carbon source downshift were investigated in Streptomyces hygroscopicus. RNA accumulation was controlled stringently during both amino acid starvation and carbon source downshift. The pool size of ppGpp increased dramatically under these conditions. However, the intracellular concentrations of nucleoside triphosphates were low and the concentration of guanosine polyphosphates was much lower than in Escherichia coli. The possible significance of this phenomenon in the regulation is discussed.

Topics: Adenosine Triphosphate; Amino Acids; Autoradiography; Bacterial Proteins; Guanosine Pentaphosphate; Guanosine Tetraphosphate; Guanosine Triphosphate; Methylglucosides; Methylglycosides; Nucleotides; RNA, Bacterial; Serine; Streptomyces