Strength of interaction between PXR and corepressor proteins. Wild-type and indicated mutant PXR expression vectors were transfected along with (A) GAL4-SMRT or (B) GAL4-NCoR together with the XREM-LUC reporter gene. Twenty-four hours post-transfection cells were treated with Rif (10 μM) or vehicle (0.1% DMSO) for an additional 24 hours. Forty-eight hours post-transfection, reporter gene activity was determined. Data are normalized to β-galactosidase activity and are reported as the avg. ± S.D. (n = 4), in which P < 0.05 (*), P < 0.01 (**), and P < 0.001 (****). WT, wild type.