Transcriptional activation. Expression vector pSG5 containing the coding sequence for RARα, PML-RAR, NPM_S-RAR, or NPM_L-RAR was transfected into CV1, HeLa, or K562 cells along with CAT reporter genes driven by the CRABP II, (TRE3)3-tk, CRBP I, mRARα2, mRARβ2, or TREp promoter elements, and RSV-luciferase. Cells were incubated in 1 μM retinoic acid or ethanol vehicle for 16 hours after transfection and harvested for luciferase and CAT activity. The values indicate the ratio of the CAT activity induced with retinoic acid compared to ethanol, normalized for transfection efficiency. The mean and standard deviations for a minimum of 2 independent transfections are shown.