FIG. 1.
SprB regulates SPI4 gene expression. (A) Comparison of PsiiA promoter activity in the wild type, a ΔsprB mutant, and a ΔsprB mutant expressing SprB from an aTc-inducible promoter on a plasmid (pSprB). pTetR denotes the empty plasmid control. Expression was induced with 50 ng/ml aTc. (B) SprB can activate the PsiiA promoter in the absence of other SPI1 genes (ΔSPI1 ΔrtsAB); the other SPI1 regulators—HilA, HilC, HilD, and RtsA—cannot. 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. (C) SprB binds to the PsiiA promoter region as determined by a coprecipitation assay using 6×His-tagged SprB. PCR was used to determine whether the PsiiA promoter region is in the coprecipitated DNA. The PfimA promoter region was included as a negative control. For an expanded description of the experimental procedures, see the supplemental material.