The multiple antibiotic resistance activator protein represses transcription of the operon.

In , the operon is a determinant for antibiotic resistance. Such phenotypes require the encoded transcription factor MarA that activates efflux pump expression. To better understand all genes controlled by MarA, we recently mapped binding of the regulator across the genome. As expected, many MarA targets were adjacent to genes encoding stress response systems. Surprisingly, one MarA-binding site overlapped the operon regulatory region. Here, we show that MarA specifically targets this locus and can block transcription of the genes. Repression is mediated by binding of MarA to a site overlapping the P1 promoter -35 element. Control of the operon by MarA does not impact antibiotic resistance.