Synthesis of the stationary-phase sigma factor sigma s is positively regulated by ppGpp.
Strains of Escherichia coli which lack detectable guanosine 3',5'-bispyrophosphate (ppGpp) display a pleiotropic phenotype that in some respects resembles that of rpoS (katF) mutants. This led us to examine whether ppGpp is a positive regulator of sigma s synthesis. sigma s is a stationary-phase-specific sigma factor that is encoded by the rpoS gene. We found that a ppGpp-deficient strain is defective in sigma s synthesis as cells enter stationary phase in a rich medium, as judged by immunoblots. Under more-defined conditions we found that the stimulation of sigma s synthesis following glucose, phosphate, or amino acid starvation of wild-type strains is greatly reduced in a strain lacking ppGpp. The failure of ppGpp-deficient strains to synthesize sigma s in response to these starvation regimens could indicate a general defect in gene expression rather than a specific dependence of rpoS expression on ppGpp. We therefore tested the effect of artificially elevated ppGpp levels on sigma s synthesis either with mutations that impair ppGpp decay or by gratuitously inducing ppGpp synthesis with a Ptac::relA fusion. In both instances, we observed enhanced sigma s synthesis. Apparently, ppGpp can activate sigma s synthesis under conditions of nutrient sufficiency as well as during entry into stationary phase. This finding suggests that changes in ppGpp levels function both as a signal of imminent stationary phase and as a signal of perturbations in steady-state growth.
Gentry
D R
DR
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Hernandez
V J
VJ
Nguyen
L H
LH
Jensen
D B
DB
Cashel
M
M
D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005798:Genes, Bacterial; D005947:Glucose / Q000378:metabolism; D006159:Guanosine Tetraphosphate / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000096:biosynthesis; D007700:Kinetics; D009154:Mutation; D010710:Phosphates / Q000378:metabolism; D010957:Plasmids; D012808:Sigma Factor / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D013997:Time Factors
D000596:Amino Acids; D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D010710:Phosphates; C079011:SigB protein, Bacteria; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D006159:Guanosine Tetraphosphate; D005947:Glucose