Characterization of ResDE-dependent fnr transcription in Bacillus subtilis

The ResD-ResE signal transduction system is required for transcription of genes involved in aerobic and anaerobic respiration in Bacillus subtilis. Phosphorylated ResD (ResD∼P) interacts with target DNA to activate transcription. A strong sequence similarity was detected in promoter regions of some ResD-controlled genes including fnr and resA. Single-base substitutions in the fnr and resA promoters were performed to determine a ResD-binding sequence. DNase I footprinting analysis indicated that ResD∼P itself does not bind to fnr, but interaction of ResD∼P with the C-terminal domain of the α subunit (αCTD) of RNA polymerase (RNAP) facilitates cooperative binding of ResD∼P and RNAP, thereby increasing fnr transcription initiation. Consistent with this result, amino acid substitutions in αCTD, such as Y263A, K267A, A269I, or N290A, sharply reduced fnr transcription in vivo, and the K267A αCTD protein, unlike the wild-type protein, did not increase ResD∼P binding to the fnr promoter. Amino acid residues of αCTD required for ResD-dependent fnr transcription, with the exception of N290, which may interact with DNA, constitute a distinct surface, suggesting that these residues likely interact with ResD∼P.