Expression of the aconitase (citB) gene of Bacillus subtilis is subject to catabolite repression in cells grown in minimal media. In nutrient broth medium, citB expression is low in growing cells but is induced when cells enter sporulation. A 600-base-pair DNA fragment that extends from positions -400 through +200, relative to the transcription start site, was shown to include all of the cis-acting sequences necessary for catabolite repression and sporulation-associated regulation. This was demonstrated by fusing this DNA fragment to the Escherichia coli lacZ gene, integrating the fusion in the amyE locus of the B. subtilis chromosome, and measuring the regulation of expression of j8-galactosidase. By creating a series of deletions from either end of the 600-base-pair fragment, it was possible to define a target for catabolite repression; at least part of this target lies within the sequence between positions -84 and -68. DNA fragments that included positions -84 through +36, when carried on high-copy plasmids, caused derepression of aconitase synthesis, as if a negative regulator were being titrated. The same plasmids caused derepression of citrate synthase activity as well. Deletion of the sequence between positions -84 and -67 abolished this titration effect for both enzymes. Mutations that altered the target for catabolite repression also affected the inducibility of citB at the onset of sporulation, at least when sporulation was induced by the addition of decoyinine, an inhibitor of guanine nucleotide synthesis. When sporulation was induced by exhaustion of nutrient broth, there was no detectable difference in expression of citl-lacZ fusions whether or not they had the citB sequence from positions -84 to -67, suggesting that the mechanisms of regulation of citB in minimal medium and nutrient broth are different.Aconitase (EC 4.2.1.3; citrate [isocitrate] hydro-lyase), an enzyme of the Krebs cycle, is subject to several forms of regulation in Bacillus subtilis. In a minimal medium containing glucose and glutamine or glutamate, the citB gene, which encodes aconitase (5), is transcribed at a low level. Transcription is increased when glucose is replaced by a poorly metabolized carbon source such as citrate. It is also increased when the medium does not contain any compound rapidly convertible to 2-ketoglutarate (2-KG) (e.g., glutamine or glutamate) (26). A hint that this phenomenon might involve a negative regulator came from the observation that aconitase expression is partially derepressed in a cell that contains multiple copies of the citB promoter region (4).A second aspect of citB regulation is related to sporulation. Addition of decoyinine, a compound that induces sporulation in a defined medium by inhibiting the synthesis of guanine nucleotides (16), causes a rapid increase in citB transcription and aconitase activity (4,33). These two aspects of regulation may be linked in that induction of citB by decoyinine is associated with a decrease in 2-KG levels (4, 9, 32). It has been shown, but only at the le...

The production of protective antigen (PA), the common component of the two anthrax toxins, is influenced by the environment. In order to examine factors involved in its regulation, a transcriptional fusion between the promoter region of the PA gene (pag) and the lacZ gene was constructed and introduced into Bacillus anthracis Sterne. Activity of the pag promoter was followed by measuring β‐galactosidase activities under various growth and medium conditions. Expression from the pag promoter was observed throughout exponential‐phase and was maximal in early stationary phase. The activity of the pag promoter was stimulated by the addition of glucose in the medium.