Effect of substitutions of QacR residues E90 and E120 on induction in vivo.

aValues, derived from the average of at least two β-lactamase reporter gene assays, are expressed in units, where 1 unit is equivalent to 1 µM of nitrocefin hydrolyzed/min at 37°C. Basal induction was measured in the absence of inducing drug and the concentrations of the QacR ligands required for maximal induction of wt QacR are 17.09 µM Et, 1.90 µM Dq, 1.25 µM MG, and 0.95 µM R6G, respectively.