The Escherichia coli Transcriptional Regulator MarA Directly Represses Transcription of purA and hdeA

Abstract

The Escherichia coli MarA protein mediates a response to multiple environmental stresses through the activation or repression in vivo of a large number of chromosomal genes. Transcriptional activation for a number of these genes has been shown to occur via direct interaction of MarA with a 20-bp degenerate asymmetric "marbox" sequence. It was not known whether repression by MarA was also direct. We found that purified MarA was sufficient in vitro to repress transcription of both purA and hdeA. Transcription and electrophoretic mobility shift experiments in vitro using mutant promoters suggested that the marbox involved in the repression overlapped the ؊35 promoter motif and was in the "backward" orientation. This organization contrasts with that of the class II promoters activated by MarA, in which the marbox also overlaps the ؊35 motif but is in the "forward" orientation. We conclude that MarA, a member of the AraC/XylS family, can act directly as a repressor or an activator, depending on the position and orientation of the marbox within a promoter.

Role of the Multidrug Resistance Regulator MarA in Global Regulation of the hdeAB Acid Resistance Operon in Escherichia coli

“…Regulation of the hdeAB operon. The figure has been produced using data from the literature (8,13,16,20,22,24,26,27,30,33,37,39,42,43,44,46) as well as the results obtained in this study. Thick arrows represent genes.…”

“…2). MarA is known to bind a "marbox" partially overlapping the Ϫ35 hexamer of the promoter (37). Therefore, competition with RNA polymerase for DNA binding and/or direct interactions between MarA and 70 , 38 , or other subunits of RNA polymerase are possible.…”

“…Putative binding sites were identified using the "search patterns" utility of Colibri (genolist.pasteur.fr/Colibri/). MarA (37) and H-NS (39) binding sites in the hdeAB promoter region have already been identified. The GadE binding site has been located between Ϫ158 and ϩ4 but not identified (20).…”

“…Using gene arrays, Pomposiello et al (33) found that overexpression of MarA from an isopropyl-␤-D-thiogalactopyranoside (IPTG)-inducible plasmid repressed hdeAB and other genes involved in acid resistance (gadA, gadB, gadC, hdeD, and slp), whereas sodium salicylate activated these same genes. Direct repression of hdeAB by MarA has been demonstrated previously (37). However, whether MarA affects cell resistance to acid conditions remained unknown.…”

Regulation of mtrF Expression in Neisseria gonorrhoeae and Its Role in High-Level Antimicrobial Resistance

“…4). Although AraC-like regulators are commonly activators of transcription, several AraClike regulators have been identified that function as both activators and repressors, including MarA in E. coli (32), YbtA (4), and PchR (11). Also similar to the repression of mtrF by MtrR, MpeR-dependent repression had no effect on the TX-100 induction of mtrF expression (Fig.…”