Transcriptional activity of wild-type and mutant receptors. (A) TRE-tk-CAT reporter or (B) βRE-tk-CAT reporter was cotransfected with the indicated receptors. pSG5 is the vector alone. Relative CAT activity with () or without (▪) 10⁻⁶ mol/L tRA treatment is shown with calculated fold induction below. Each data point represents results from three independent transfections. (C) The βRE-tk-CAT reporter was cotransfected with PML-RARα m4 and RARα wt expression vectors. The ratio of PML-RARα m4 to RARα was varied, and the total amount of receptor plasmids was kept at 0.7 μg for each transfection.