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, 311 (1), 36-43

Transcriptional Regulation of the mexEF-oprN Multidrug Efflux Pump Operon by MexT and an Unidentified Repressor in nfxC-type Mutant of Pseudomonas Aeruginosa

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Transcriptional Regulation of the mexEF-oprN Multidrug Efflux Pump Operon by MexT and an Unidentified Repressor in nfxC-type Mutant of Pseudomonas Aeruginosa

Hideaki Maseda et al. FEMS Microbiol Lett.

Abstract

Expression of the MexEF-OprN efflux pump in Pseudomonas aeruginosa seems to be upregulated by MexT. The region upstream of the mexEF-oprN operon contains mexT arranged in tandem with mexEF-oprN and separated by 230 bp of mexT-mexE intergenic DNA. Therefore, it is likely that this intergenic DNA contains the promoter-operator element of mexEF-oprN. To characterize how the expression of the mexEF-oprN operon was controlled, we analyzed the mexT-mexE intergenic DNA by constructing a series of intergenic DNA deletions connected with the mexE∷lacZ reporter and made two important discoveries. The first was that the central region of the DNA contained two nod boxes. The mexT-proximal nod box was identified as the MexT-binding site by gel-shift assays using purified MexT. The mexT-distal nod box was required for the transcription of the mexEF-oprN operon, but not for the binding of MexT, suggesting that this region accommodates the binding of the RNA polymerase. The second observation is that there is a 13 bp inverted repeat sequence separated by 10 bp immediately upstream of the mexE gene. Deletion of this region caused a sudden rise in MexEF-OprN production, suggesting that this region accommodates the binding of a putative repressor protein.

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