Autoactivation of the marRAB multiple antibiotic resistance operon by the MarA transcriptional activator in Escherichia coli
- 1 April 1996
- journal article
- research article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 178 (8) , 2216-2223
- https://doi.org/10.1128/jb.178.8.2216-2223.1996
Abstract
Transcriptional activation of the promoters of the mar/soxRS regulons by the sequence-related but independently inducible MarA and SoxS proteins renders Escherichia coli resistant to a broad spectrum of antibiotics and superoxide generators. Here, the effects of MarA and SoxS on transcription of the marRAB promoter itself were assayed in vitro by using a minimal transcription system and in vivo by assaying beta-galactosidase synthesized from marR::lacZ fusions. Purified MarA and MalE-SoxS proteins stimulated mar transcription about 6- and 15-fold, respectively, when the RNA polymerase/DNA ratio was 1. Purified MarA bound as a monomer to a 16-bp "marbox" located 69 to 54 nucleotides upstream of a putative RNA initiation site. Deletion of the marbox reduced MarA-mar binding 100-fold, abolished the stimulatory effects of MarA and SoxS on transcription in vitro, and reduced marR::lacZ synthesis about 4-fold in vivo. Deletion of upstream DNA adjoining the marbox reduced MarA binding efficiency 30-fold and transcriptional activation 2- to 3-fold, providing evidence for an accessory marbox. Although MarA and the mar operon repressor, MarR, bound to independent sites, they competed for promoter DNA in band shift experiments. Assays of marR::lacZ transcriptional fusions in marRAB deletion or soxRS deletion strains showed that the superoxide generator paraquat stimulates mar transcription via soxRS and that salicylate stimulates mar transcription both by antagonizing MarR and by a MarR-independent mechanism. Thus, transcription of the marRAB operon is autorepressed by MarR and autoactivated by MarA at a site that also can be activated by SoxS.Keywords
This publication has 38 references indexed in Scilit:
- Ambidextrous transcriptional activation by SoxS: requirement for the C‐terminal domain of the RNA polymerase alpha subunit in a subset of Escherichia coli superoxide‐inducible genesMolecular Microbiology, 1996
- Binding of purified multiple antibiotic-resistance repressor protein (MarR) to mar operator sequences.Proceedings of the National Academy of Sciences, 1995
- Genes acrA and acrB encode a stress‐induced efflux system of Escherichia coliMolecular Microbiology, 1995
- Purification of a MaIE‐SoxS fusion protein and identification of the control sites of Escherichia coli superoxide‐inducible genesMolecular Microbiology, 1994
- Two genetically-distinct and differentially-regulated aconitases (AcnA and AcnB) in Escherichia coliMicrobiology, 1994
- Genetic relationship between soxRS and mar loci in promoting multiple antibiotic resistance in Escherichia coliAntimicrobial Agents and Chemotherapy, 1994
- The XylS/AraC family of regulatorsNucleic Acids Research, 1993
- Fumarase C, the stable fumarase of Escherichia coli, is controlled by the soxRS regulon.Proceedings of the National Academy of Sciences, 1992
- Isolation of gene fusions (soi::lacZ) inducible by oxidative stress in Escherichia coli.Proceedings of the National Academy of Sciences, 1988
- Improved single and multicopy lac-based cloning vectors for protein and operon fusionsGene, 1987