Fig. 1.

(a) Scheme of phoBR regulatory region fragments used in this work. Pho boxes are represented by black rectangles; mutation in box 2 is represented by a gray rectangle. (b) EMSA pattern of the phoBR 234-bp regulatory region fragment radiolabeled with ³²P by PhoB binding. In the left panel, 50 fmol of the fragment was incubated with increasing concentrations of purified PhoB (1.5, 2, 2.5, 3, 3.5, 4, 8, 12, 16, 20, and 32 μM). In the first lane, the FP (free probe) position is indicated by a solid arrow; dotted arrows point to three distinct shifted bands. In the right panel is the result of the competition assay using 50 fmol of radiolabeled 234-bp promoter fragment and PhoB at 32 μM against 50, 250, and 500 fmol of unlabeled probe.