Interaction of H-NS and ToxT with ctx promoter DNA. Competitive gel mobility shift assays were carried out with the ctx promoter fragment (C2; −202 to +114) by combining various amounts of H-NS and ToxT. (A) Fixed amounts of H-NS with increasing levels of ToxT. H-NS was added at 0 (lanes 1 and 4 to 6), 0.165 (lanes 2 and 7 to 9), and 0.33 μM (lanes 3 and 10 to 12), followed by addition of ToxT at 0 (lanes 1 to 3), 0.9 (lanes 4, 7, and 10), 1.8 (lanes 5, 8, and 11), and 3.6 μM (lanes 6, 9, and 12). (B) Fixed amounts of ToxT with increasing levels of H-NS. ToxT was added at 0 (lanes 1 and 4 to 6), 1.8 (lanes 2 and 7 to 9), and 3.6 μM (lanes 3 and 10 to 12), followed by addition of H-NS at 0 (lanes 1 to 3), 0.165 (lanes 4, 7, and 10), 0.33 (lanes 5, 8, and 11), and 0.66 μM (lanes 6, 9, and 12).