FIG. 6.
ExsA stimulates formation of open complexes as measured by potassium permanganate footprinting. (A and B) Supercoiled minicircles carrying the PexsC (A) or PexsD (B) promoter (1.6 nM) were incubated in the absence (−) or presence (+) of ExsAHis (30 nM) for 10 min. RNAP was added to the indicated concentrations and incubated for 3 min. Reaction mixtures were then treated with potassium permanganate (except for the control [KMnO4]), and the modified minicircles were used as templates in primer extension reactions with a radiolabeled coding-strand primer. Primer extension products were subjected to denaturing electrophoresis and phosphorimaging. Dideoxy sequencing reactions for A and T are indicated. The diagrams to the left show the transcriptional start sites (bold), the −10 regions (boxed), and the nucleotides modified by potassium permanganate (indicated with asterisks).