A vitamin D analogue containing an affinity and a photoaffinity probe (affinity-driven cross- linker, Double Label) was synthesized. An unknown factor, associated with vitamin D receptor (VDR), was isolated from rat liver nuclear extract using a GST-VDR-ligand-binding domain fusion protein (GST-VDR-LBD), affinity labeled with Double Label, and protein– protein cross-linking by photolysis.
