Characterization of a Bacillus subtilis sporulation operon that includes genes for an RNA polymerase sigma factor and for a putative DD-carboxypeptidase.

Abstract

At early stages of sporulation, the spoIIA locus is transcribed as a tricistronic (1.7-kb) operon, coding for sigma F and for two proteins that modulate the activity of sigma F. The locus is transcribed as a longer (2.9-kb) transcript at the late stages of sporulation. We show here that the longer transcript contains an additional open reading frame whose product has extensive sequence homology with DD-carboxypeptidases; the corresponding gene is designated dacF. Cotranscription of a morphogene, such as dacF, with the gene for a sigma factor suggests a way to couple transcription regulation with morphogenesis. The predicted N-terminal sequence of the DacF protein and the inhibition of sporulation by a translational dacF-lacZ fusion both suggest that the protein has a signal peptide for transport into or across a membrane. Expression of a dacF-lacZ transcriptional fusion was in the forespore. The 5' end of the 2.9-kb transcript was determined by primer extension analysis. The region 5' to the end showed no homology to promoters recognized by known sigma factors but was homologous to the corresponding region of the forespore-specific 0.3-kb gene of Bacillus subtilis.