THE MTRR REPRESSOR BINDS THE DNA-SEQUENCE BETWEEN THE MTRR AND MTRC GENES OF NEISSERIA-GONORRHOEAE

Gonococcal resistance to antimicrobial hydrophobic agents (HAs) is due to energy-dependent removal of HAs from the bacterial cell by the Mtr CDE membrane-associated efflux pump. The mtrR (multiple transferrable resistance Regulator) gene encodes a putative transcriptional represso r protein (MtrR) believed to be responsible for regulation of mtrCDE g ene expression. Gel mobility shift and DNase I footprint assays that u sed a maltose-binding protein (MBP)-MtrR fusion protein demonstrated t hat the MtrR repressor is capable of specifically binding the DNA sequ ence between the mtrR and mtrC genes. This binding site was localized to a 26-nucleotide stretch that includes the promoter utilized for mtr CDE transcription and, on the complementary strand, a 22-nucleotide st retch that contains the -35 region of the mtrR promoter. A single tran sition mutation (A-->G), within the MtrR-binding site decreased the af finity of the target DNA for MtrR and enhanced gonococcal resistance t o HAs when introduced into HA-susceptible strain FA19 by transformatio n. Since this mutation enhanced expression of the mtrCDE gene complex but decreased expression of the mtrR gene, the data are consistent wit h the notion that MtrR acts as a transcriptional repressor of the mtrC DE efflux pump protein genes.