THE BACILLUS-SUBTILIS REGULATOR SINR INHIBITS SPOLLG PROMOTER TRANSCRIPTION IN-VITRO WITHOUT DISPLACING RNA-POLYMERASE

Initiation of sporulation in Bacillus subtilis controlled by several r egulators which affect activation by phosphorylation of the key respon se regulator SpoOA or transcription of SpoOA similar to P-dependent ge nes. 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 stud y we have demonstrated that in vitro SinR directly repressed SpoOA sim ilar to P-dependent transcription by B.subtilis RNA polymerase from th e spollG operon promoter. SinR inhibited transcription prior to format ion of heparin-resistant complexes but did not displace RNA polymerase from the spollG promoter. DNase I protection studies demonstrated tha t SinR protected a large region of the spollG; promoter and induced DN ase I hypersensitive sites, particularly around the OA boxes, at the s ame positions as those induced by zinc. Since binding of zinc induces bends In the DNA, we concluded that SinR binding also altered the conf ormation of the spollG promoter. We propose that SinR-induced conforma tional changes in SpoOA-dependent promoters prevent activation of tran scription by SpoOA similar to P.