FIG. 1.

DcuR-dependent regulation of the dcuB operator-promoter region. (A) The dcuB operator-promoter region is shown together with a summary of gel retardation experiments performed with DcuR and the indicated DNA fragments. Asterisks indicate those fragments that were specifically retarded by DcuR. The coordinates for each fragment are given with respect to the previously defined +1 site (11). The promoter and predicted Fnr and Crp sites are indicated by gray boxes. The experimentally determined location of the DcuR-binding site is indicated by the hatched box. (B and C) The indicated segments of the dcuB operator-promoter region were used to construct multicopy dcuB-lacZ transcriptional fusions (Table 1; also see Materials and Methods for details). Expression (in micromoles of o-nitrophenyl-β-d-galactopyranoside per minute per gram of protein) was tested anaerobically in M9 medium containing glycerol, Casamino Acids, and TMAO, with (+) or without (−) fumarate (for panel C, the fumarate-free medium included nitrate).