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Catalytic Function of an α/β Hydrolase Is Required for Energy Stress Activation of the ςB Transcription Factor inBacillus subtilis

ABSTRACT The general stress response of Bacillus subtilis is controlled by the ςB transcription factor, which is activated in response to diverse energy and environmental stresses. These two classes of stress are transmitted by separate signaling pathways which converge on the direct regulators of ςB, the RsbV anti-anti-ς factor and the RsbW anti-ς factor. The energy signaling branch involves the RsbP phosphatase, which dephosphorylates RsbV in order to trigger the general stress response. ThersbP structural gene lies downstream fromrsbQ in a two-gene operon. Here we identify the RsbQ protein as a required positive regulator inferred to act in concert with the RsbP phosphatase. RsbQ bound RsbP in the yeast two-hybrid system, and a large in-frame deletion in rsbQ had the same phenotype as a null allele of rsbP—an inability to activate ςB in response to energy stress. Genetic complementation studies indicated that this phenotype was not due to a polar effect of the rsbQ alteration onrsbP. The predicted rsbQ product is a hydrolase or acyltransferase of the α/β fold superfamily, members of which catalyze a wide variety of reactions. Notably, substitutions in the presumed catalytic triad of RsbQ also abolished the energy stress response but had no detectable effect on RsbQ structure, synthesis, or stability. We conclude that the catalytic activity of RsbQ is an essential constituent of the energy stress signaling pathway.