FIG. 4.

cifR negatively regulates cif gene expression. cif gene and Cif protein expression were assayed using either sqRT-PCR or Western blotting, respectively. (A) The wild type (WT), the Δcif mutant, and the ΔPA2931 mutant harboring the empty vector pMQ71 or expressing the PA2931 gene from the plasmid pDPM79 were assayed for cif and rplU gene expression. Deletion of the PA2931 gene resulted in higher levels of cif gene transcript, which was complemented by expression of the histidine-tagged variant of PA2931. (B) Western blot of the WT P. aeruginosa strain PA14, the ΔPA2931 mutant containing the empty vector pMQ71, and the ΔPA2931 mutant carrying a plasmid expressing a histidine-tagged variant of PA2931 from the arabinose-inducible expression plasmid pDPM79. Arabinose was added to a final concentration of 0.2% where indicated.