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Journal of Bacteriology, August 1999, p. 4853-4862, Vol. 181, No. 16
Department of Microbiology and Immunology,
West Virginia University Health Sciences Center, Morgantown, West
Virginia 26506
Received 13 April 1999/Accepted 15 June 1999
The RpoS sigma factor of enteric bacteria is either required for or
augments the expression of a number of genes that are induced during
nutrient limitation, growth into stationary phase, or in response to
stresses, including high osmolarity. RpoS is regulated at multiple
levels, including posttranscriptional control of its synthesis, protein
turnover, and mechanisms that affect its activity directly. Here, the
control of RpoS stability was investigated in Salmonella
typhimurium by the isolation of a number of mutants specifically
defective in RpoS turnover. These included 20 mutants defective in
mviA, the ortholog of Escherichia coli rssB/sprE, and 13 mutants defective in either clpP or
clpX which encode the protease active on RpoS. An
hns mutant was also defective in RpoS turnover, thus
confirming that S. typhimurium and E. coli have
identical genetic requirements for this process. Some current models
predict the existence of a kinase to phosphorylate the response
regulator MviA, but no mutants affecting a kinase were recovered. An
mviA mutant carrying the D58N substitution altering the
predicted phosphorylation site is substantially defective, suggesting
that phosphorylation of MviA on D58 is important for its function. No
evidence was obtained to support models in which acetyl phosphate or
the PTS system contributes to MviA phosphorylation. However, we did
find a significant (fivefold) elevation of RpoS during exponential
growth on acetate as the carbon and energy source. This behavior is due
to growth rate-dependent regulation which increases RpoS synthesis at
slower growth rates. Growth rate regulation operates at the level of
RpoS synthesis and is mainly posttranscriptional but, surprisingly, is
independent of hfq function.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
RpoS Synthesis Is Growth Rate Regulated in Salmonella
typhimurium, but Its Turnover Is Not Dependent on Acetyl
Phosphate Synthesis or PTS Function
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, P.O. Box 9177, WVU Health Sciences Center, Morgantown, WV 26506-9177. Phone: (304) 293-2676. Fax: (304) 293-7823. E-mail: telliott{at}wvu.edu.
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