The 414-bp EcoRI-HindIII Z81 fragments containing the abrB coding region were labeled at their EcoRI ends. A, Abh binding reactions performed at pH 7 (lanes 1–5) versus pH 8 (lanes 6 –9). Lanes 1 and 6, 30 μM Abh; lanes 2 and 7, 10 μM Abh; lanes 3 and 8, 3 μM Abh; lanes 4, 5, and 9, no Abh. B, wild-type AbrB and AbrB(E30A) binding to Z81 at pH 8. Lane 1, 20 μM wild type; lane 2, 2 μM wild type; lane 3, 7 μM E30A; lane 4, 0.7 μM E30A; lane 5, no protein. Two positions showing limited Abh-afforded protection are marked a and b (see “Results”). Maxam-Gilbert purine (R) and pyrimidine (Y) sequencing ladders are shown for reference. *, artifactual lane between lanes 8 and 9.