Negative regulation of sigma 54-dependent dctA expression by the transcriptional activator DctD

In Rhizobium meliloti, the presence of the C4-dicarboxylate transport protein DctA is required for symbiotic N2 fixation in alfalfa root nodules. Expression of dctA is inducible and is mediated by a sensor and activator gene pair encoded by dctB and dctD. In the presence of C4-dicarboxylates, the DCTB sensor protein is believed to phosphorylate and activate DCTD, which in turn activates transcription at the sigma 54-dependent dctA promoter. …