ChIP assays to detect the effect of ATRA on the in vivo association of the nuclear receptors for retinoic acid with the repressor region in the FR-β promoter. KG-1 cells were treated with 1 μM ATRA for 24 hours and subjected to ChIP assays as described in “Materials and methods.” In all panels: lane 1, 50-bp DNA ladder; lanes 2, 4, 6, and 8, KG-1 cells treated with vehicle; lanes 3, 5, 7, and 9, KG-1 cells treated with ATRA; lanes 4 and 5, primers amplifying an irrelevant region in the FR-β gene; lanes 6 and 7, normal rabbit IgG used for immunoprecipitation negative control; and lanes 8 and 9, input DNA used as template for PCR. (A) Effect of ATRA on the association of RARα with the repressor region in the FR-β gene. Antibody specific for RARα was used in lanes 2 to 5. (B) Effect of ATRA on the association of RARβ with the repressor region in the FR-β gene. Antibody specific for RARβ was used in lanes 2 to 5. (C) Effect of ATRA on the association of RARγ with the repressor region in the FR-β gene. Antibody specific for RARγ was used in lanes 2 to 5. Each experiment was repeated at least 4 times and concordant results were obtained.