Rhizobium meliloti DctD, a σ54‐dependent transcriptional activator, may be negatively controlled by a subdomain in the C‐terminal end of its two‐component receiver module

Rhizobium meliloti DctD is believed to have three functional domains: an N‐terminal, two‐component receiver domain; and like other σ54‐dependent activators, C‐terminal and central domains for DNA binding and transcription activation. We have characterized a progressive series of M‐terminal deletions of R meliloti DctD. The N‐terminal domain was not needed for binding the dctA upstream activation sequence. Only 25% of the C‐terminal end of the receiver domain was needed to significantly inhibit the central domain, and proteins lacking up to 60% of the N‐terminal end of the receiver domain were‘inducible’in R. meliloti cells. We hypothesize that the W‐terminal two‐thirds of the DctD receiver domain augments and controls an adjacent subdomain for inhibiting the central domain.