FIG. 2.

HilA regulates SprB expression. (A) HilA can activate the P_sprB promoter in the absence of other SPI1 genes (ΔSPI1 ΔrtsAB); the other SPI1 regulators—HilC, HilD, and RtsA—cannot. SprB was also found not to regulate its own expression. Activators were expressed from an aTc-inducible promoter on a plasmid. Expression was induced with 50 ng/ml aTc. Fluorescence values were normalized with the optical density at 600 nm (OD600; A.U., arbitrary units) to account for cell density. Error bars indicate standard deviations. (B) HilA binds to the P_sprB promoter region as determined by a coprecipitation assay with 6×His-tagged HilA. PCR was used to determine whether the P_sprB promoter region is in the coprecipitated DNA. The P_prgH and P_fimA promoter regions were included as positive and negative controls, respectively. For an expanded description of the experimental procedures, see the supplemental material.