Identification and characterization of a stress-responsive promoter in themacromolecular synthesis operon of Bacillus subtilis

Bacillus subtilis DB1005 is a temperature-sensitive (Ts) sigA mutant. Induc tion of sigma(A) has been observed exclusively in this mutant harbouring ex tra copies of the plasmid-borne Ts sigA gene transcriptionally controlled b y the P1P2 promoters of the B. subtilis macromolecular synthesis (MMS; rpoD or sigA) operon. Investigation of the mechanisms leading to the induction has allowed us to identify a sigma(B)-type promoter, P7, in the MMS operon for the first time. Therefore, at least seven promoters in total are respon sible for the regulation of the B. subtilis MMS operon, including the four known sigma(A)- and sigma(H)-type promoters, as well as two incompletely de fined promoters. The P7 promoter was activated in B. subtilis after the imp osition of heat, ethanol and salt stresses, indicating that the MMS operon of B. subtilis is subjected to the control of general stress. The significa nt heat induction of P7 in B. subtilis DB1005 harbouring a plasmid-borne Ts sigA gene can be explained by a model of competition between sigma(A) and sigma(B) for cove binding; very probably, the sigma(B) factor binds more ef ficiently to core RNA polymerase under heat shock. This mechanism may provi de a means for the expression of the B. subtilis MMS operon when CTA become s defective in core binding.