Control of intracellular serine protease expression in Bacillus subtilis

Expression of the major intracellular serine protease (ISP-1) gene of Bacillus subtilis was studied by using a translational fusion plasmid in which the isp promoter region was fused to the lacZ gene. beta-Galactosidase activity, used to measure transcription from the isp promoter, was produced immediately after the end of exponential growth, whereas intracellular protease activity was not detected until 4 h later. These results are consistent with a previous suggestion that ISP-1 initially accumulates in the cell in an enzymatically inactive form. ISP-1 activity was detected in all of the sporulation-deficient strains examined, and the amount of protease activity always corresponded to the amount of beta-galactosidase activity. These results indicate that the activation of ISP-1 is not dependent on a sporulation-specific gene product. Expression of ISP-1 is regulated by a number of mutations known to affect the expression of extracellular enzymes. In sacU(h) and sacQ(h) mutants, the expression of ISP-1 was 10-fold higher than in the wild-type strain. In catA, hpr, and scoC strains, expression of ISP was stimulated two- to threefold, whereas in sacU mutants the expression of ISP-1 was reduced to less than 10% of the wild-type level. The temporal expression and activation of ISP-1 was not affected by any of these mutations. This is the first evidence that the expression of a native intracellular protein is affected by these hyperproduction mutations.