THE BACILLUS-SUBTILIS RSBU GENE-PRODUCT IS NECESSARY FOR RSBX-DEPENDENT REGULATION OF SIGMA(B)

sigma(B) is a secondary a factor of Bacillus subtilis. sigma(B)-depend ent transcription is induced when B. subtilis enters the stationary ph ase of growth or is exposed to any of a number of different environmen tal stresses. Three genes (rsbV, rsbW, and rsbX), which are cotranscri bed with the sigma(B) structural gene (sigB), encode regulators of sig ma(B)-dependent gene expression. RsbW and RsbV have been shown to cont rol sigma(B) activity, functioning as an inhibitory sigma(B) binding p rotein and its antagonist, respectively, Using the SPAC promoter (P-SP AC) to control the expression of the sigB operon, a ctc::lacZ reporter system to monitor sigma(B) activity, and monoclonal antibodies to det ermine the levels of sigB operon products, we have now obtained eviden ce that RsbX is an indirect regulator of sigma(B) activity, Genetic da ta and in vivo measurements argue that RsbX negatively regulates an ex tension of the RsbV-RsbW pathway that requires the product of an addit ional regulatory gene (rsbU) which lies immediately upstream of the si gB operon, The results are consistent with RshU, or a process dependen t on RsbU, being able to facilitate the RsbV-dependent release of sigm a(B) from RsbW but normally prevented from doing this by RsbX.