FIG 7.

PhoP binds to the promoter of slrP. (A) Two fragments of DNA containing the promoter region of slrP, −460/+21 and −139/+21, were inserted into plasmid pIC552 to generate lacZ transcriptional fusions. These plasmids and derivatives carrying the indicated point mutations were introduced into S. enterica serovar Typhimurium strain 14028 (wild type) or a phoP-null mutant, and β-galactosidase activities were measured in cultures grown to stationary phase in liquid LPM. Means and standard deviations from two independent β-galactosidase measurements are shown. (B) Purified His₆-PhoP was phosphorylated in vitro using acetyl phosphate. DNA fragments containing the promoter region of slrP, the same region with a point mutation (T-40C), and the promoter regions of slyB and phoN, as positive and negative controls, respectively, were PCR amplified using fluorochrome-labeled primers and incubated with the indicated concentrations of phosphorylated His₆-PhoP (His₆-PhoP-P). Slot blotting was used to quantify binding. Results from a representative experiment of three independent experiments are shown.