The start point for transcription of the subtilisin (aprE) gene was determined by primer extension analysis and was found to be at a point significantly different from that identified in a previously published report (S. L. Wong, C. W. Price, D. S. Goldfarb, and R. H. Doi, Proc. Natl. Acad. Sci. USA 81:1184-1188, 1984). An aprE-lacZ fusion was used to analyze expression of the promoter. Deletion analyses of the promoter were performed to determine the extent of the upstream region necessary for activity. This was found to be between -52 and -41 with respect to the transcription start site. Expression of the aprE-lacZ fusion was unimpaired in a mutant deleted for the sigma B subunit of RNA polymerase. Mutations in the gene for the sigma H subunit of RNA polymerase decreased expression of the aprE-lacZ fusion to approximately 25% of that of the wild type. These results leave the identity of the sigma factor responsible for transcription of this gene in question. Mutations in the spo0A gene drastically decreased the activity of the aprE promoter and its upstream deletion derivatives, while the abrB gene, a phenotypic suppressor of spo0 mutations, restored activity of the aprE promoter in all of the deletion derivatives. Thus, inhibition of transcription by the spo0A mutation and its restoration by an abrB mutation could not be separated from the promoter of the aprE gene.