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

At early stages of sporulation, the spoIIA locus is transcribed as a tricistronic (1.7-kb) operon, coding for σ(F) and for two proteins that modulate the activity of σ(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 σ 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 σ factors but was homologous to the corresponding region of the forespore-specific 0.3-kb gene of Bacillus subtilis.