Identification of the porcine intestinal accessory factor that enables DNA sequence recognition by vitamin D receptor.

The nuclear accessory protein in porcine intestinal nuclear extracts that activates the binding of the vitamin D receptor to its vitamin D response elements has been highly purified. It contains a protein that binds 9-cis-[3H]retinoic acid, was detected on immunoblots with an anti-retinoid X receptor (RXR) peptide antibody, and supports the binding of retinoic acid receptor gamma to the retinoic acid receptor beta gene response element. Most important, the two specific complexes formed by porcine nuclear extract with the vitamin D response elements from either the osteocalcin gene or the rat 24-hydroxylase gene are shifted to a larger complex by both an anti-vitamin D receptor antibody and an anti-RXR antibody, leaving no doubt that in vivo the nuclear accessory factor for the vitamin D receptor in the intestine is an RXR protein.