Branched pattern of regulatory interactions between late sporulation genes in Bacillus subtilis.

We measured the synthesis of dipicolinic acid (DPA) during sporulation in spo mutants of Bacillus subtilis by a sensitive biological assay based on cross-feeding of a spoVF mutant strain and also chemically. Many spo mutations, including several that block sporulation at stage III, did not prevent synthesis of DPA but instead prevented its incorporation into the spore. In general, strains with mutations in loci that are expressed in the spore compartment synthesized DPA, whereas strains with mutations in most of the loci that are expressed in the mother-cell compartment did not. Transcription of the gerE gene, as measured by DNA-RNA hybridization, followed a dependence pattern very similar to that of DPA synthesis. However, the dependence patterns of the two operons show that at about stage IV of sporulation there is a branch in the sequence of operon expression in the mother cell. One branch leads through spoVC to synthesis of DPA synthetase, and the other leads through spoVD to expression of gerE.