FIG. 3.
MarR repressor activity assayed in the PmarII::lacZ reporter strain E. coli SPC105 (marR+). Cells were grown at 37°C to mid-logarithmic phase in LB broth, without glucose, containing the appropriate antibiotics and IPTG (50 μM) and sodium salicylate (5 mM) where appropriate. β-Galactosidase assays were performed with cells permeabilized with chloroform-SDS as previously described (17, 20). The relative β-galactosidase activities (±standard deviations) in the absence (open bars) or presence (hatched bars) of 5 mM sodium salicylate are presented. Activities were determined for the host strain alone (None), the wild-type MarR (WT), and other MarR proteins that show a superrepressor phenotype (mutations are indicated below each bar).