Rhizobium meliloti DctD, a sigma 54-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 sigma 54-dependent activators, C-terminal and central domains for DNA binding and transcription activation. We have characterized a progressive series of N-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 receive 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 N-terminal two-thirds of the DctD receiver domain augments and controls an adjacent subdomain for inhibiting the central domain.