Fig. 5. CpxR-P binds to the pap promoter. (A) Schematic of the pap promoter region (top) and the model of transcriptional inactivation, phase OFF (center), and activation, phase ON (bottom) (adapted from van der Woude et al., 1996). Phase variation is affected by the action of DAM on the adenines in the two DNA GATC sequences, designated GATC-I and GATC-II, contained within the Lrp binding sites 5 and 2, respectively (explained in text). Abbreviations: CAP, catabolite activator protein; Lrp, leucine-responsive regulatory protein. The involvement of CpxR is discussed in the text. (B) Schematic of strategy for DNA probes used in EMSAs. Only probe 3 contains the putative CpxR binding site; probes 1 and 2 do not. A positive control probe, DegP, encoding the previously identified CpxR binding site in the degP promoter was also used in the EMSAs. (C) EMSAs of His₆-CpxR binding to the putative site in the pap promoter. His₆-CpxR was purified and phosphorylated. Unphosphorylated (His₆-CpxR) or phosphorylated His₆-CpxR (His₆-CpxR-P) was incubated with DNA probes from (B) and run on 4% acrylamide gels.