Transcriptional regulation of the mexEF-oprN multidrug efflux pump operon by MexT and an unidentified repressor in nfxC-type mutant of Pseudomonas aeruginosa

FEMS Microbiol Lett. 2010 Oct;311(1):36-43. doi: 10.1111/j.1574-6968.2010.02063.x. Epub 2010 Aug 18.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Outer Membrane Proteins / genetics*
  • Bacterial Outer Membrane Proteins / metabolism
  • Gene Expression Regulation, Bacterial*
  • Mutation
  • Operon*
  • Protein Binding
  • Pseudomonas aeruginosa / drug effects
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Transcription, Genetic*


  • Bacterial Outer Membrane Proteins
  • OprN protein, Pseudomonas aeruginosa
  • Repressor Proteins