Use of a lacZ gene fusion to determine the dependence pattern of sporulation operon spoIIIC in spo mutants of Bacillus subtilis: a branched pathway of expression of sporulation operons.

The sporulation gene spoIIIC from Bacillus subtilis was fused to the lacZ gene from Escherichia coli, so that the transcription of the lacZ gene was under the control of the spoIIIC promoter. Production of beta-galactosidase, under conditions of sporulation, was then used as an indicator to study the expression of spoIIIC in relation to other sporulation loci. Expression of spoIIIC, which occurred only in the mother cell compartment, was prevented by mutations in all of the stage 0 and stage II loci, and also by spoIIID, spoIVA and spoIVB mutations. By contrast, the last three operons are not needed for expression of spoVA, which has previously been shown to be spore-specific. In consequence, a branched pathway of gene expression is proposed. One branch leads to expression of spoVA within the spore compartment, the other to expression of spoIIIC in the mother cell.