Journal of Bacteriology, May 1999, p. 2846-2851, Vol. 181, No. 9
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Center for Tuberculosis Research,
Received 29 December 1998/Accepted 22 February 1999
SigB, a newly discovered alternative sigma factor of
Staphylococcus aureus, has been shown to play an important
role in stress responses and the regulation of virulence factors. The
rsbW (orf159) gene is immediately upstream of
sigB. Its gene product is homologous to Bacillus
subtilis RsbW which under appropriate conditions binds to
B. subtilis SigB and functions as an anti-sigma factor or
negative posttranslational regulator. To define the function of
S. aureus RsbW, both the S. aureus SigB and
RsbW proteins were expressed in Escherichia coli and
purified. Cross-linking experiments with these purified proteins
revealed that RsbW was capable of specific binding to SigB. In an in
vitro transcription runoff assay, RsbW prevented SigB-directed
transcription from the sar P3 promoter, a known
SigB-dependent promoter, and the inhibitory activity of RsbW was found
to be concentration dependent. We also identified SigB promoter
consensus sequences upstream of the genes encoding alkaline shock
protein 23 and coagulase and have demonstrated SigB and RsbW dependence
for the promoters in vitro. These results show that RsbW is a protein
sequestering anti-sigma factor of S. aureus SigB and
suggest that SigB activity in S. aureus is regulated posttranslationally.
*
Corresponding author. Mailing address: Center for
Tuberculosis Research, Johns Hopkins School of Public Health, 615 N. Wolfe St., Baltimore, MD 21205-2179. Phone: (410) 955-3507. Fax: (410) 614-8173. E-mail: wbishai{at}jhsph.edu.
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