Binding of CebR-H to the cebE promoter region. (A) CebR-H used in this study was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lane 1, crude extract of E. coli BL21(DE3)Gold cells harboring pET-CebR; lane 2, purified CebR-H; lane 3, molecular mass standards (phosphorylase b [94 kDa], bovine serum albumin [67 kDa], ovalbumin [43 kDa], carbonic anhydrase [30 kDa], and soybean trypsin inhibitor [20 kDa]). (B) EMSA using CebR-H and a DNA fragment containing the cebE promoter region. The CebR-H homodimer was diluted stepwise by 75% from 57 nM (lane 2) to 1.4 nM (lane 15). Lane 1 shows a negative control without CebR-H. The positions of free probe (solid arrowhead) and DNA-CebR-H complexes (open arrowhead) are shown. (C) Plot of percentages of CebR-H-bound probe versus log[CebR-H (nM)] from 18 nM (lane 6) to 3.2 nM (lane 12). The apparent Kd value for CebR-H is indicated by a dashed line.