SUMMARY: 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-deoxyg I uconate kinase; kdgA, encoding 2-keto-3-deoxyg luconate-6-phosphate aldolase; and kdg, encoding a transporter. These four genes are organized in one transcriptional unit and map at 198" of the B. subtik chromosome. Primer extension experiments and Northern blot analysis show that an active σ-dependent promoter precedes kdgR and transcription is terminated at the putative pindependent terminator downstream of kdgr. The operon is negatively regulated by the kdgR and ccpA gene products, which belong t o the Lac1 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.


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