Mammalian 2-hybrid analysis of interaction between RARα and N-CoR following treatment with ATRA and/or G/GM-CSF. Cotransfection of pGAL4-N-CoR, pGAL4(UAS)₅-tk-luc, pVP16-RARα1, and pMB1-CMV-lacZ for internal control were performed in U-937 cells and luciferase activity was measured 18 hours after treatment with indicated agents. Results represent the mean (numbers above bars) ± SD of 2 independent experiments done in triplicates. Control cotransfection of an empty GAL4(DBD) vector with pVP16-RARα did not result in activation of the GAL4(UAS)₅tk-luc gene expression (data not shown). The statistical significance of differences between control and treated samples is indicated by asterisks, and between treated samples by plus symbols. ^***/+++P < .001, ^**/++P < .01, ^*/+P < .05.