The Mar proteins are involved in the multiple antibiotic resistance, a non-specific resistance system. The expression of the mar operon is controlled by a repressor, MarR. A large number of compounds induce transcription of the mar operon. This is thought to be due to the compound binding to MarR, and the resulting complex stops MarR binding to the DNA. With the MarR repression lost, transcription of the operon proceeds [1]. The structure of MarR is known [2] and shows MarR as a dimer with each subunit containing a winged-helix DNA binding motif.

1: The Salmonella typhimurium mar locus: molecular and genetic analyses and assessment of its role in virulence. Sulavik MC, Dazer M, Miller PF; J Bacteriol 1997;179:1857-1866. PMID:9068629

2: The crystal structure of MarR, a regulator of multiple antibiotic resistance, at 2.3 A resolution. Alekshun MN, Levy SB, Mealy TR, Seaton BA, Head JF; Nat Struct Biol 2001;8:710-714. PMID:11473263