Genetic and functional analysis of the multiple antibiotic resistance (mar) locus in Escherichia coli

Abstract

A 7.8-kbp fragment of chromosomal DNA from a region controlling multiple antibiotic resistance (Mar) in Escherichia coli has been sequenced. Within the fragment is a potential divergent promoter region including marO, which contains two pairs of direct repeats, suggesting possible operator-regulatory sites. To the left of marO (region I) are one or two transcriptional units with three putative open reading frames (ORFs) encoding 64, 157, and 70 amino acids. To the right (region II) is a transcriptional unit containing three putative ORFs (0RF125/144, 0RF129, and 0RF72). Of six independent Mar mutants, four had mutations within the ORF encoding the first putative protein (0RF125/144) downstream of marO, including three different single-point mutations and an IS2 insertion. One of the other mutations occurred in marO (20-bp duplication), and the other occurred in a site in marO or 0RF144 (a 1-bp change). All six mutations led to increased transcription of the region II transcript. High-copy-number plasmids containing marO and the adjacent 0RF125/144 region from a wild-type source but not from a Mar mutant reduced the antibiotic resistance of a Mar mutant to levels comparable to those of wild-type cells. High-copy-number plasmids containing wild-type marO alone caused an increase in resistance to tetracycline, chloramphenicol, and norfloxacin in a wild-type strain. The nature of the Mar mutations and the results of the complementation studies suggest that 0RF125/144 encodes a repressor (designated MarR) which acts at marO. The second ORF (0RF129), designated marA, would encode a protein, MarA, whose sequence shows strong similarity to those of a family of positive transcriptional regulators. A TnS insertion in marA inactivated the multiresistance phenotype of Mar mutants. The function of 0RF72, designated marB, encoding the third putative protein in the operon, and that of other ORFs detected within the 7.8-kb fragment have not yet been determined.

Characterization of a cationic surfactant-resistant mutant isolated spontaneously from Escherichia coli

“…Such a pleiotropic mutation in a regulatory gene causing multi-drug resistance has been reported in mar mutants of E. coli (Cohen et al 1989(Cohen et al , 1993. In these mutants, both reduction of the outer membrane permeability and suppression of OmpF synthesis were observed, as in strain OW66 described in this study.…”

Genetic definition of the Escherichia coli zwf "soxbox," the DNA binding site for SoxS-mediated induction of glucose 6-phosphate dehydrogenase in response to superoxide

“…SoxS is a member of the AraC subfamily of helix-turn-helix proteins (1,13,41). Within this subfamily, the proteins encoded by soxS (1,41), tetD (4,31), marA (6,7), and rob (37) are highly homologous to one another over the entire 107-amino-acid length of SoxS, with the extent of homology ranging from 42% identity for the SoxS-MarA pair to 59% identity for the TetD-Rob pair. Even more striking is the fact that among the four proteins, at least three have the identical amino acid at 17 of the 21 positions of the respective helix-turn-helix motifs and at 10 of the 11 positions of the turn and the second, recognition helix.…”

“…Indeed, E. coli strains deleted for zwf are hypersensitive to oxidative stress, thus making zwf a pivotal member of the soxRS regulon (18, 21). In addition, treatment of cells with several antibiotics and aromatic weak acids appears to activate zwf transcription through the action of marA, thus making zwf a member of the multiple antibiotic resistance (mar) regulon (2,6,7,14,16).…”

Expression of a Butyrivibrio fibrisolvens E14 gene (cinB) encoding an enzyme with cinnamoyl ester hydrolase activity is negatively regulated by the product of an adjacent gene (cinR)

“…5). PecS (Reverchon et al, 1994), Hpr (Perego & Hoch, 1988), HpcR (Roper et al, 1993), EmrR (del Castillo et al, 1991) and MarR (Cohen et al, 1993) have all been shown to be negative regulators of bacterial gene expression. The B. fibrisoluens sequence is most similar to HpcR, a negative regulator of the homoprotocatechuate degradative operon of E. coli C (Roper et al, 1993), and PecS, a negative regulator of pectinase, cellulase and blue pigment production in Erwinia chrysantherni (Reverchon et al, 1994), with 31 Yo and 26 '/o amino acid identity respectively.…”