EmrR, the repressor of the emrRAB operon of Escherichia coli, was purified
to 95% homogeneity. EmrR was found to bind putative ligands of the EmrAB pu
mp-2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, and carbony
l cyanide p- (trifluoro-methoxy) phenylhydrazone-with affinities in the mic
romolar range. Equilibrium dialysis experiments suggested one bound ligand
per monomer of the dimeric EmrR.