Abstract: We investigated the organization and expression of the Bacillus subtilis sigY operon, the first gene of which codes for sigmaY, a member of the extracytoplasmic function (ECF) family of sigma factors. The sigY operon, comprising six genes (sigY, yxlC, D, E, F, and G), was induced upon nitrogen starvation; it was continuously transcribed from the 31st base upstream of sigY to a neighboring convergent gene, yxlH, resulting in a 4.2-kb mRNA. The expression of the sigY operon was also positively autoregulated through sigmaY, suggesting that its transcription is likely to be directed by sigmaY. Deletion analysis of the sigY promoter, which was localized by primer extension, revealed the promoter region of sigY with the "-10" and "-35" sequences of CGTC and TGAACG, respectively. The latter sequence was distinct from those recognized by sigmaW, sigmaX, and sigmaM. The sigmaY-directed transcription of sigY was under negative regulation involving YxlD. sigY disruption affected sporulation induced by nitrogen starvation, but sigY induction upon nitrogen starvation was not associated with the sporulation process. The organization and function of the sigY operon are significantly conserved in several microorganisms living in adverse living environments.