The Bacillus subtilis SinR protein is a repressor of the key sporulation gene spo0A.

SinR is a pleiotropic DNA binding protein that is essential for the late-growth processes of competence and motility in Bacillus subtilis and is also a repressor of others, e.g., sporulation and subtilisin synthesis. In this report, we show that SinR, in addition to being an inhibitor of sporulation stage II gene expression, is a repressor of the key early sporulation gene spo0A. The sporulation-specific rise in spo0A expression at time zero is absent in a SinR-overproducing strain and is much higher than normal in strains with a disrupted sinR gene. This effect is direct, since SinR binds specifically to spo0A in vitro, in a region overlapping the -10 region of the sporulation-specific Ps promoter that is recognized by E-sigma H polymerase. Methyl interference and site-directed mutagenesis studies have identified guanine residues that are important for SinR recognition of this DNA sequence. Finally, we present evidence that SinR controls sporulation through several independent genes, i.e., sp0A, spoIIA, and possibly spoIIG and spoIIE.     

Expression in Bacillus subtilis of the Bacillus thuringiensis cryIIIA toxin gene is not dependent on a sporulation-specific sigma factor and is increased in a spo0A mutant.

Expression of the Bacillus thuringiensis cryIIIA gene encoding a Coleoptera-specific toxin is weak during vegetative growth and is activated at the onset of the stationary phase. cryIIIA'-'lacZ fusions and primer extension analysis show that the regulation of cryIIIA expression is similar in Bacillus subtilis and in B. thuringiensis. Activation of cryIIIA expression was not altered in B. subtilis mutant strains deficient for the sigma H and sigma E sporulation-specific sigma factors or for minor sigma factors such as sigma B, sigma D, or sigma L. This result and the nucleotide sequence of the -35 and -10 regions of the cryIIIA promoter suggest that cryIIIA expression might be directed by the E sigma A form of RNA polymerase. Expression of the cryIIIA'-'lacZ fusion is shut off after t2 (2 h after time zero) of sporulation in the B. subtilis wild-type strain grown on nutrient broth sporulation medium. However, no decrease in cryIIIA-directed beta-galactosidase activity occurred in sigma H, kinA, or spo0A mutant strains. Moreover, beta-galactosidase activity was higher and remained elevated after t2 in the spo0A mutant strain. beta-Galactosidase activity was weak in abrB and spo0A abrB mutant strains, suggesting that AbrB is responsible for the higher level of cryIIIA expression observed in a spo0A mutant. However, both in spo0A and spo0A abrB mutant strains, beta-galactosidase activity remained elevated after t2, suggesting that even in the absence of AbrB, cryIIIA expression is controlled through modulation of the phosphorylated form of Spo0A. When the cryIIIA gene is expressed in a B. subtilis spo0A mutant strain or in the 168 wild-type strain, large amounts of toxins are produced and accumulate to form a flat rectangular crystal characteristic of the coleopteran-specific B. thuringiensis strains.