Journal of Bacteriology, February 2001, p. 1329-1338, Vol. 183, No. 4
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.4.1329-1338.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
B of Bacillus subtilis


Department of Food Science and Technology, University of California, Davis, California 95616,1 and Department of Genetics, Trinity College, Dublin 2, Ireland2
Received 12 September 2000/Accepted 26 November 2000
Expression of the general stress regulon of Bacillus
subtilis is controlled by the alternative transcription factor
B, which is activated when cells encounter
growth-limiting energy or environmental stresses. The RsbT
serine-threonine kinase is required to convey environmental stress
signals to
B, and this kinase activity is magnified in
vitro by the RsbR protein, a positive regulator important for full in
vivo response to salt or heat stress. Previous genetic analysis
suggested that RsbR function is redundant with other unidentified
regulators. A search of the translated B. subtilis genome
found six paralogous proteins with significant similarity to RsbR:
YetI, YezB, YkoB, YojH, YqhA, and YtvA. Their possible regulatory roles
were investigated using three different approaches. First, genetic
analysis found that null mutations in four of the six paralogous genes
have marked effects on the
B environmental signaling
pathway, either singly or in combination. The two exceptions were
yetI and yezB, adjacent genes which appear to
encode a split paralog. Second, biochemical analysis found that YkoB,
YojH, and YqhA are specifically phosphorylated in vitro by the RsbT
environmental signaling kinase, as had been previously shown for RsbR,
which is phosphorylated on two threonine residues in its C-terminal
region. Both residues are conserved in the three phosphorylated
paralogs but are absent in the ones that were not substrates of RsbT:
YetI and YezB, each of which bears only one of the conserved residues;
and YtvA, which lacks both residues and instead possesses an N-terminal
PAS domain. Third, analysis in the yeast two-hybrid system suggested
that all six paralogs interact with each other and with the RsbR and
RsbS environmental regulators. Our data indicate that (i) RsbR, YkoB,
YojH, YqhA, and YtvA function in the environmental stress signaling
pathway; (ii) YtvA acts as a positive regulator; and (iii) RsbR, YkoB, YojH, and YqhA collectively act as potent negative regulators whose
loss increases
B activity more than 400-fold in
unstressed cells.
Present address: Department of Microbiology and Molecular Genetics,
Harvard Medical School, Boston, MA 02115.
Present address: Department of Food Science and Technology,
Youngdong University, Chungbuk 370-800, Korea.
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