The kdgRKAT operon of Bacillus subtilis: detection of the transcript and regulation by the kdgR and ccpA genes.

Transcription of a new catabolic operon in Bacillus subtilis, involved in the late stages of galacturonic acid utilization, has been studied. The operon consists of four genes: kdgR, encoding the putative regulator protein; kdgK, encoding 2-keto-3-deoxygluconate kinase; kdgA, encoding 2-keto-3-deoxygluconate-6-phosphate aldolase; and kdgT, encoding a transporter. These four genes are organized in one transcriptional unit and map at 198 degrees of the B. subtilis chromosome. Primer extension experiments and Northern blot analysis show that an active sigmaA-dependent promoter precedes kdgR and transcription is terminated at the putative p-independent terminator downstream of kdgT. The operon is negatively regulated by the kdgR and ccpA gene products, which belong to the LacI family of transcription regulators. The expression of the genes in this operon can be induced by galacturonate and strongly repressed when glucose is present in the growth medium. Knockout mutations in genes kdgR and ccpA remove, respectively, the effects of galacturonate and glucose on the transcription of this operon.