AphB binds to the toxR promoter region to regulate toxR gene expression. (A) Three different lengths of toxR promoter regions used in (B) were PCR amplified and cloned into pBBRlux containing a transcriptional lux reporter. The level of Lux induction with pBAD-aphB compared to pBAD24 in E. coli in the presence of 0.01% arabinose is given in the table. Alignment of putative AphB binding sites in tcpP, aphB, and toxR promoter region is given. (B) Gel shift assays using purified MBP-AphB and DNA containing various lengths of the regulatory regions of the toxR promoter. Protein concentrations used in the gel shift assay (shown as shaded triangles) were 0, 20, 40, 80 ng/reaction (5 μl).