Nuclear receptor for calcitriol, the active form of vitamin D3 which mediates the action of this vitamin on cells. Enters the nucleus upon vitamin D3 binding where it forms heterodimers with the retinoid X receptor/RXR. The VDR-RXR heterodimers bind to specific response elements on DNA and activate the transcription of vitamin D3-responsive target genes. Recruited to promoters via its interaction with BAZ1B/WSTF which mediates the interaction with acetylated histones, an essential step for VDR-promoter association. Plays a central role in calcium homeostasis. Homodimer in the absence of bound vitamin D3. Heterodimer with RXRA after vitamin D3 binding. Localizes mainly to the nucleus. Translocated into the nucleus via both ligand-dependent and ligand-independent pathways; ligand-independent nuclear translocation is mediated by IPO4. Detected in all tissues examined. Highest level in small intestine and skin. First detected at stage 13. Increases gradually and peaks at stage 57-61 then decreases to the level seen in adult. Composed of three domains: a modulating N-terminal domain, a DNA-binding domain and a C-terminal ligand-binding domain. The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. Belongs to the nuclear hormone receptor family. NR1 subfamily.