NPM_S-RAR inhibits transcriptional activation by RAR. HeLa or U937 cells were transfected with mRARβ2-CAT and a luciferase transfection control along with equimolar amounts of pSG5 + RARα, PML-RAR + RARα, or NPM_S-RAR + RARα. 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.