NarL-dependent expression of nrdR.
A) Representation of the P. aeruginosa PAO1 nrdR promoter region sequence, indicating the different mutated NarL binding sites. Black boxes indicate the putative NarL recognition sites, and mutated sequences are shown in upper case and in bold letters. The transcription start site is indicated in bold. The RFU column shows the relative fluorescence intensity presented by the P. aeruginosa wild-type nrdR promoter fusion (pETS161), compared with their mutated NarL boxes (pETS181, pETS182 and pETS183 for NarL box1, pETS184, pETS185 and pETS186 for NarL box2, and pEST187 harboring the double mutation). The expression of wild-type nrdR promoter under a ΔnarL mutant background is also stated. The ratio column shows a comparison of all the conditions with the expression of a wild-type promoter under a wild-type background. Strains were grown anaerobically until the mid-logarithmic phase. Values represent the mean of three independent experiments. Transcriptional start codon is shown in bold. Three independent experiments were performed and the mean±standard deviation is shown). *: Significantly different compared with wild-type promoter region (pETS161) in an unpaired t-test (P<0.05).