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Expression of the multidrug resistance operon mexA-mexB-oprM in Pseudomonas aeruginosa: mexR encodes a regulator of operon expression.
Antimicrob Agents Chemother. 1996 Sep; 40(9):2021-8.AA

Abstract

The region upstream of the multiple antibiotic resistance efflux operon mexA-mexB-oprM in Pseudomonas aeruginosa was sequenced, and a gene, mexR, was identified. The predicted MexR product contains 147 amino acids with a molecular mass of 16,964 Da, which is consistent with the observed size of the overexpressed mexR gene product. MexR was homologous to MarR, the repressor of MarA-dependent multidrug resistance in Escherichia coli, and other repressors of the MarR family. A mexR knockout mutant showed a twofold increase in expression of both plasmid-borne and chromosomal mexA-reporter gene fusions compared with the MexR+ parent strain, indicating that the mexR gene product negatively regulates expression of the mexA-mexB-oprM operon. Furthermore, the cloned mexR gene product reduced expression of a plasmid-borne mexA-lacZ fusion in E. coli, indicating that MexR represses mexA-mexB-oprM expression directly. Consistent with the increased expression of the efflux operon in the mexR mutant, the mutant showed an increase (relative to its MexR+ parent) in resistance to several antimicrobial agents. Expression of a mexR-lacZ fusion increased threefold in a mexR knockout mutant, indicating that mexR is negatively autoregulated. OCR1, a nalB multidrug-resistant mutant which overproduces OprM, exhibited a greater than sevenfold increase in expression of a chromosomal mexA-phoA fusion compared with its parent. Introduction of a mexR knockout mutation in strain OCR1 eliminated this increase in efflux gene expression and, as expected, increased the susceptibility of the strain to a variety of antibiotics. The nucleotide sequences of the mexR genes of OCR1 and its parental strain revealed a single base substitution in the former which would cause a predicted substitution of Trp for Arg at position 69 of its mexR product. These data suggest that MexR possesses both repressor and activator function in vivo, the activator form being favored in nalB multidrug-resistant strains.

Authors+Show Affiliations

Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, Canada. poolek@post.queensu.caNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

8878574

Citation

Poole, K, et al. "Expression of the Multidrug Resistance Operon mexA-mexB-oprM in Pseudomonas Aeruginosa: mexR Encodes a Regulator of Operon Expression." Antimicrobial Agents and Chemotherapy, vol. 40, no. 9, 1996, pp. 2021-8.
Poole K, Tetro K, Zhao Q, et al. Expression of the multidrug resistance operon mexA-mexB-oprM in Pseudomonas aeruginosa: mexR encodes a regulator of operon expression. Antimicrob Agents Chemother. 1996;40(9):2021-8.
Poole, K., Tetro, K., Zhao, Q., Neshat, S., Heinrichs, D. E., & Bianco, N. (1996). Expression of the multidrug resistance operon mexA-mexB-oprM in Pseudomonas aeruginosa: mexR encodes a regulator of operon expression. Antimicrobial Agents and Chemotherapy, 40(9), 2021-8.
Poole K, et al. Expression of the Multidrug Resistance Operon mexA-mexB-oprM in Pseudomonas Aeruginosa: mexR Encodes a Regulator of Operon Expression. Antimicrob Agents Chemother. 1996;40(9):2021-8. PubMed PMID: 8878574.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Expression of the multidrug resistance operon mexA-mexB-oprM in Pseudomonas aeruginosa: mexR encodes a regulator of operon expression. AU - Poole,K, AU - Tetro,K, AU - Zhao,Q, AU - Neshat,S, AU - Heinrichs,D E, AU - Bianco,N, PY - 1996/9/1/pubmed PY - 1996/9/1/medline PY - 1996/9/1/entrez SP - 2021 EP - 8 JF - Antimicrobial agents and chemotherapy JO - Antimicrob. Agents Chemother. VL - 40 IS - 9 N2 - The region upstream of the multiple antibiotic resistance efflux operon mexA-mexB-oprM in Pseudomonas aeruginosa was sequenced, and a gene, mexR, was identified. The predicted MexR product contains 147 amino acids with a molecular mass of 16,964 Da, which is consistent with the observed size of the overexpressed mexR gene product. MexR was homologous to MarR, the repressor of MarA-dependent multidrug resistance in Escherichia coli, and other repressors of the MarR family. A mexR knockout mutant showed a twofold increase in expression of both plasmid-borne and chromosomal mexA-reporter gene fusions compared with the MexR+ parent strain, indicating that the mexR gene product negatively regulates expression of the mexA-mexB-oprM operon. Furthermore, the cloned mexR gene product reduced expression of a plasmid-borne mexA-lacZ fusion in E. coli, indicating that MexR represses mexA-mexB-oprM expression directly. Consistent with the increased expression of the efflux operon in the mexR mutant, the mutant showed an increase (relative to its MexR+ parent) in resistance to several antimicrobial agents. Expression of a mexR-lacZ fusion increased threefold in a mexR knockout mutant, indicating that mexR is negatively autoregulated. OCR1, a nalB multidrug-resistant mutant which overproduces OprM, exhibited a greater than sevenfold increase in expression of a chromosomal mexA-phoA fusion compared with its parent. Introduction of a mexR knockout mutation in strain OCR1 eliminated this increase in efflux gene expression and, as expected, increased the susceptibility of the strain to a variety of antibiotics. The nucleotide sequences of the mexR genes of OCR1 and its parental strain revealed a single base substitution in the former which would cause a predicted substitution of Trp for Arg at position 69 of its mexR product. These data suggest that MexR possesses both repressor and activator function in vivo, the activator form being favored in nalB multidrug-resistant strains. SN - 0066-4804 UR - https://www.unboundmedicine.com/medline/citation/8878574/Expression_of_the_multidrug_resistance_operon_mexA_mexB_oprM_in_Pseudomonas_aeruginosa:_mexR_encodes_a_regulator_of_operon_expression_ L2 - http://aac.asm.org/cgi/pmidlookup?view=long&pmid=8878574 DB - PRIME DP - Unbound Medicine ER -