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FEMS Microbiol Lett. 2004 Sep 1;238(1):23-8.

MexZ-mediated regulation of mexXY multidrug efflux pump expression in Pseudomonas aeruginosa by binding on the mexZ-mexX intergenic DNA.

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Department of Molecular Life Science, Tokai University School of Medicine, 145 Shimokasuya, Isehara-shi, Kanagawa-ken 259-1193, Japan.


MexZ is a transcriptional regulator of the mexXY multidrug transporter operon, which confers aminoglycoside resistance on Pseudomonas aeruginosa. Highly purified MexZ showed direct binding with a specific site of the mexZ-mexX intergenic DNA when probed by a gel retardation assay. Both in vitro chemical cross-linking experiments and an in vivo two-hybrid expression system showed that the active form of MexZ, which is capable of binding the intergenic DNA, appeared to be a dimer. These results explain the mechanism by which MexZ represses transcription of the mexXY operon, but do not explain the substrate-induced hyperproduction of MexXY. The presence of inducer antibiotic in the gel-retardation assay mixture failed to detect altered MexZ-probe DNA interaction suggesting the possible involvement of an additional regulator.

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