Gain-of-function mutation of sapB that affects formation of alkaline phosphatase by Bacillus subtilis in sporulation conditions.

The sapB locus was defined by mutations that render sporulation alkaline phosphatase formation independent of sigma F and sigma E without affecting the temporal control of formation. The sapB locus has been cloned and sequenced. The deduced polypeptide is 232 amino acids long, with a molecular mass of 26 kDa. It is very similar to four sequences in the database, none of which has a known function. Analysis of the transcription of sapB indicates that it is induced during late exponential phase, and that maximum expression is reached during the first hour of stationary phase, both under sporulation and non-sporulation conditions. The defining mutations of the locus, sapB2 and sapB10, have been sequenced and found to contain the same change, a G-->A transition resulting in an Ala111 Thr switch. This mutation apparently results in a gain-of-function, as sapB null mutants are indistinguishable from sap+ strains in terms of their APase production during sporulation.