Catalytic Function of an Alpha/beta Hydrolase is Required for Energy Stress Activation of the Sigma(B) Transcription Factor in Bacillus Subtilis

The general stress response of Bacillus subtilis is controlled by the sigma(B) 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 sigma(B), the RsbV anti-anti-sigma factor and the RsbW anti-sigma factor. The energy signaling branch involves the RsbP phosphatase, which dephosphorylates RsbV in order to trigger the general stress response. The rsbP structural gene lies downstream from rsbQ 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 sigma(B) in response to energy stress. Genetic complementation studies indicated that this phenotype was not due to a polar effect of the rsbQ alteration on rsbP. The predicted rsbQ product is a hydrolase or acyltransferase of the alpha/beta 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.