FIGURE 9.

AccR controls the activity of the P_D promoter under anaerobic conditions. A and B, Azoarcus sp. CIB (CIB) and Azoarcus sp. CIBΔaccR (CIBΔaccR) cells were grown aerobically (A) or anaerobically (B) in minimal medium containing 3 mm benzoate (black bars) or a mixture of 3 mm benzoate and 0.2% succinate (white bars) until mid-exponential phase. Transcripts from the P_D promoter were measured by real-time RT-PCR. Graphed values (in arbitrary units) are the average from three independent experiments ± S.D. (error bars). C, gel retardation analyses of P_D probe as in Fig. 3B. Assays were performed with increasing concentrations (0–12 μm) of carbamoyl phosphate-treated His₆-AccR (AccR-P). The free P_D probe and the major P_D·AccR-P complex are indicated by arrows. D, sequence alignment of AccR binding regions in different catabolic promoters of Azoarcus sp. CIB. P_N (OR2), operator region 2 of the P_N promoter; P_N (OR1), operator region 1 of the P_N promoter; P_D, P_D promoter of the box cluster; P_B1, P_B1 promoter of the mbd cluster. A consensus sequence of the AccR operator is shown at the bottom. Nucleotides identical to the consensus are shown in boldface type.