CcpC, a novel regulator of the LysR family required for glucose repressionof the citB gene in Bacillus subtilis

Synergistic carbon catabolite repression of the Bacillus subtilis aconitase (citB) gene by glucose and a source of 2-ketoglutarate is dependent on DNA sequences located upstream of the gene. Mutations in a dyad symmetry eleme nt centered at position -66 and in a repeat of the downstream arm of the dy ad symmetry at position -27 cause derepressed citB expression. In this work , a protein able to bind to a DNA fragment containing these elements was pu rified and identified. This protein, named CcpC (Catabolite control protein C), shares sequence similarity with members of the LysR family of transcri ptional regulators. In addition to binding to the citB promoter, CcpC bound to the promoter of the citZ gene, which encodes the cell's major citrate s ynthase and is subject to carbon catabolite repression. In a ccpC null muta nt, expression of both citB and citZ was derepressed in glucose-glutamine m inimal medium, indicating that CcpC is a negative regulator of citB and cit Z gene expression. DNase I footprinting experiments showed that CcpC binds to two sites within the citB promoter region, corresponding to the dyad sym metry and -27 elements. In the presence of citrate, a putative inducer, onl y the dyad symmetry element was fully protected by CcpC. When the dyad symm etry element was mutated, CcpC was no longer able to bind to either the dya d symmetry or -27 elements. Repression of citB and citZ gene expression dur ing anaerobiosis also proved to be mediated by CcpC. (C) 2000 Academic Pres s.