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J. Bacteriol., Jul 1996, 3701-3709, Vol 178, No. 13
A Dufour, U Voelker, A Voelker and WG Haldenwang
sigma B is a secondary sigma factor that controls the general stress
response in Bacillus subtilis. sigma B-dependent genes are activated when
sigma B is released from an inhibitory complex with an anti-sigma B protein
(RsbW) and becomes free to associate with RNA polymerase. Two separate
pathways, responding either to a drop in intracellular ATP levels or to
environmental stress (e.g., heat, ethanol, or salt), cause the release of
sigma B from RsbW. rsbR, rsbS, rsbT, and rsbU are four genes now recognized
as the upstream half of an operon that includes sigB (sigma B) and its
principal regulators. Using reporter gene assays, we find that none of
these four genes are essential for stationary-phase (i.e., ATP-dependent)
activation of sigma B, but rsbU and one or more of the genes contained
within an rsbR,S,T deletion are needed for stress induction of sigma B. In
other experiments, Western blot (immunoblot) analyses showed that the
levels of RsbR, RsbS, Rsb, and RsbU, unlike those of the sigB operon's four
downstream gene products (RsbV, RsbW, RsbX and sigma B), are not elevated
during sigma B activation. Gel filtration and immunoprecipitation studies
did not reveal the formation of complexes between any of the four upstream
sigB operon products and the products of the downstream half of the operon.
Much of the detectable RsbR, RsbS, RsbT, and RsbU did, however, fractionate
as a large-molecular-mass (approximately 600-kDa) aggregate which was
excluded from our gel filtration matrix. The downstream sigB operon
products were not present in this excluded material. The unaggregated RsbR,
RsbS, and RsbU, which were retarded by the gel matrix, elated from the
column earlier than expected from their molecular weights. The RsbR and
RsbS fractionation profile was consistent with homodimers (60 and 30 kDa,
respectively), while the RsbU appeared larger, suggesting a protein complex
of approximately 90 to 100 kDa.
Copyright © 1996, American Society for Microbiology
Relative levels and fractionation properties of Bacillus subtilis sigma(B) and its regulators during balanced growth and stress
Department of Microbiology, University of Texas Health Science Center at San Antonio, Texas 78284-7758, USA.
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