Nuclear receptor for calcitriol, the active form of vitamin D3 which mediates the action of this vitamin on cells (PubMed:17227670). Enters the nucleus upon vitamin D3 binding where it forms heterodimers with the retinoid X receptor/RXR (By similarity). The VDR-RXR heterodimers bind to specific response elements on DNA and activate the transcription of vitamin D3-responsive target genes (By similarity). Plays a central role in calcium homeostasis (PubMed:17227670). Homodimer in the absence of bound vitamin D3 (By similarity). Heterodimer with RXRA after vitamin D3 binding (By similarity). Interacts with MED1 and NCOA6 (PubMed:10866662, PubMed:15065852, PubMed:17227670). Interacts with MED1, NCOA1, NCOA2, NCOA3 and NCOA6 coactivators, leading to a strong increase of transcription of target genes (By similarity). Interacts with the corepressor NCOR1 (By similarity). Interacts with SNW1 (By similarity). Interacts with IRX4, the interaction does not affect its transactivation activity (By similarity). Interacts with CRY1 (By similarity). Interacts with CRY2 in a ligand-dependent manner (By similarity). 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 intestine and kidney. 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.