Affiliation:
1. Department of Food Science and Technology, University of California, Davis, California 95616,1 and
2. Department of Genetics, Trinity College, Dublin 2, Ireland2
Abstract
ABSTRACT
Expression of the general stress regulon of
Bacillus subtilis
is controlled by the alternative transcription factor ς
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 ς
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 ς
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 ς
B
activity more than 400-fold in unstressed cells.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
139 articles.
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