THE VITAMIN-D-RECEPTOR INTERACTS WITH GENERAL TRANSCRIPTION FACTOR-IIB

The vitamin D receptor (VDR) heterodimerizes with retinoid X receptors (RXR) on many vitamin D-responsive promoter elements, suggesting that this complex is the active factor in vitamin D-mediated transcription . However, the mechanism of transcriptional regulation following VDR . RXR binding to DNA is not well characterized, Using a yeast two-hybri d protein interaction assay, we demonstrate that VDR forms specific pr otein: protein contacts with the basal transcription factor TFIIB, Del etion analysis indicated that the carboxyl terminal ligand binding dom ain of VDR interacted with a 43-residue amino-terminal domain in TFIIB . The interaction with TFIIB showed selectivity for the ligand binding domain of VDR as similar regions of RXR alpha or of retinoic acid rec eptor cu did not couple with TFIIB. Binding assays with purified prote ins showed a direct inter action between VDR and TFIIB in vitro. These data suggest a mechanism for VDR-dependent transcription in which pro tein contacts between VDR and TFIIB may impart regulatory information to the transcription preinitiation complex.