The Bacillus subtilis regulator SinR inhibits spollG promoter transcription in vitro without displacing RNA polymerase

Initiation of sporulation in Bacillus subtilis controlled by several regulators which affect activation by phosphorylation of the key response regulator SpoOA or transcription of SpoOA similar to P-dependent genes. In vivo overexpression of one of these regulators, sinR, results in suppression of transcription from the SpoOA similar to P-dependent promoters of spoOA, spollA, spollE and spollG and in vitro SinR binds to the promoters of the spollA operon and the spoOA gene. In this study we have demonstrated that in vitro SinR directly repressed SpoOA similar to P-dependent transcription by B.subtilis RNA polymerase from the spollG operon promoter. SinR inhibited transcription prior to formation of heparin-resistant complexes but did not displace RNA polymerase from the spollG promoter. DNase I protection studies demonstrated that SinR protected a large region of the spollG; promoter and induced DNase I hypersensitive sites, particularly around the OA boxes, at the same positions as those induced by zinc. Since binding of zinc induces bends In the DNA, we concluded that SinR binding also altered the conformation of the spollG promoter. We propose that SinR-induced conformational changes in SpoOA-dependent promoters prevent activation of transcription by SpoOA similar to P.