Structure and function in a Bacillus subtilis sporulation-specific sigma factor: molecular nature of mutations in spoIIAC.

The spoIIAC gene was cloned from chromosomal DNA of seven spoIIAC mutants of Bacillus subtilis, and the complete sequence of the gene was determined for each mutant. Three of the mutants proved to have chain-terminating mutations (one of which, previously shown to be suppressible by sup-3, was identified as amber); these led in every case to complete failure either to manufacture spores or to synthesize two enzymes normally associated with stage II of sporulation. The four remaining mutations were missense, and these corresponded to a phenotype in which a few spores are formed and about half the wild-type quantities of the two enzymes are made. Of the four missense mutations, two were near the promoter-distal end of the gene, in a region believed to correspond to the DNA-binding domain of the sigma factor that spoIIAC encodes. The remaining two mutations were in the region of the gene that is thought to correspond to the domain of the protein that interacts with core RNA polymerase.