Gel mobility shift assay for the binding of the HlyU protein to the VV20481-VV20480-rtxA1 promoter region. (A) Location of the DNA probes (a, b, c, and d). (B) The labeled DNA probe d (4 nM) was mixed with increasing amounts of the HlyU protein. Lanes 1 to 6 contain, respectively, 0, 10, 50, 90, 150, 300 nM HlyU. (C) For competition analysis, the unlabeled specific DNA was used as a competitor. Before the addition of 150 nM HlyU, increasing amounts of unlabeled competitor DNAs were added to the reaction containing a 4 nM concentration of the labeled DNA probe. Lanes 1 to 4 contain, respectively, 1, 10, 50, and 300 nM unlabeled competitor DNAs.