FIG. 4.

Selective interaction of the OCT-VDR-RXR heterodimer bound to VDREs with SRC-1/TIF2 family proteins. EMSA analysis was performed with [γ-³²P]ATP-labeled VDREs (DR3, and opn-VDRE). rVDR and mRXRα were expressed in transfected COS-1 cells, and the nuclear extracts therefrom were used for this assay. Bacterially expressed SRC-1 and TIF2 fused to GST were purified with glutathione-Sepharose beads, and SRC-1 and TIF2 were excised from the fusion protein. These proteins were incubated at room temperature with approximately 10 ng of labeled DR3 or opn-VDRE in the absence or presence of 10⁻⁷ M 1α,25(OH)₂D₃ (lanes 3, 6, 9, 13, 16, and 19) or OCT (lanes 4, 7, 10, 14, 17, and 20).