Fig. 7. DNase I protection of the pilin promoter with purified CtrA∼P. Purified CtrA was phosphorylated with MBP–EnvZ fusion protein in vitro in a reaction mixture containing ATP. A sequence ladder generated using the pilinrev2 primer was used to identify the protected bases. (A) In the absence of ATP, no protected regions were observed. CtrA concentrations in the footprint reactions are indicated. (B) Three distinct regions of the promoter were protected with CtrA∼P and are marked with a solid black line. These protected regions coincide with CtrA binding motifs in the pilA promoter shown in Figure 6A.