SEPARATE MECHANISMS ACTIVATE SIGMA(B) OF BACILLUS-SUBTILIS IN RESPONSE TO ENVIRONMENTAL AND METABOLIC STRESSES

sigma(B) is a secondary sigma factor that controls the general stress response of Bacillus subtilis. sigma(B)-dependent transcription is ind uced by the activation of sigma(B) itself, a process that involves rel ease of sigma(B) from an inhibitory complex,vith its primary regulator , RsbW. sigma(B) becomes available to RNA polymerase when RsbW forms a complex with an additional regulatory protein (RsbV) and, because of this, fails to bind sigma(B). Using Western blot (immunoblot) analyses , reporter gene fusion assays, and measurements of nucleotide pool siz es, we provide evidence for two independent processes that promote the binding of RsbW to RsbV. The first occurs during carbon limitation or entry into stationary phase. Activation of sigma(B) under these circu mstances correlates with a drop in the intracellular levels of ATP and may be a direct consequence of ATP levels on RsbW's binding preferenc e. The second activation process relies on the product of a third regu latory gene, rsbU. RsbU is dispensable for sigma(B) activation during carbon limitation or stationary phase but is needed for activation of sigma(B) in response to any of a number of different environmental ins ults (ethanol treatment, salt or acid shock, etc.). RsbU, or a process dependent on it, alters RsbW binding without regard for intracellular levels of ATP. In at least some instances, the effects of multiple in ducing stimuli are additive. The data are consistent with RsbW being a regulator at which distinct signals from separate effecters can be in tegrated to modulate sigma(B) activity.