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J. Bacteriol. doi:10.1128/JB.00050-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Regulators of the Bacillus subtilis cydABCD operon: Identification of a negative regulator, CcpA, and a positive regulator, ResD

Laboratory for Molecular Biology, Department of Biological Sciences, University of Illinois at Chicago, Illinois 60607, USA

^* To whom correspondence should be addressed. Email: Hulett{at}uic.edu.

	Abstract

The cydABCD operon of Bacillus subtilis encodes products required for the production of cytochrome bd oxidase. Previous work has shown that one regulatory protein, YdiH (Rex), is involved in the repression of this operon. Work reported here confirms the role of Rex in the negative regulation of the cydACBD operon. Two additional regulatory proteins for the cydABCD operon were identified; ResD, a response regulator involved in the regulation of respiration genes, and CcpA, the carbon catabolite regulator protein. ResD, but not ResE, was required for full expression of the cydA promoter in vivo. ResD binding to the cydA promoter between -58 to -107, a region which includes ResD consensus binding sequences, was not enhanced by phosphorylation. A ccpA mutant had increased expression from the full length cydA promoter during stationary growth compared to the wild type strain. Maximal expression in a ccpA mutant was observed from a 3' deleted cydA promoter fusion that lacks the Rex binding region, suggesting that the effect of the two repressors, Rex and CcpA, was cumulative. CcpA binds directly to the cydA promoter protecting a region, -4 to -33, that contains sequences similar to the CcpA consensus binding sequence, cre box. CcpA binding was enhanced upon addition of glucose-6-phosphate, a putative cofactor for CcpA. Mutation of a conserved residue in the cre box reduced CcpA binding 10 fold in vitro and increased cydA expression in vivo. Thus CcpA and ResD, along with the previously identified cydA regulator, Rex (YdiH), affect the expression of the cydABCD operon. Low-level induction of the cydA promoter was observed in vivo in the absence of its regulatory proteins, Rex, CcpA and ResD. This complex regulation suggests that the cydA promoter is tightly regulated to allow its expression only at the appropriate time and under the appropriate conditions.