Figure 4. Model of the vitamin D receptor (VDR). The N terminal region is short relative to other steroid hormone receptors. This region is followed by two zinc fingers which constitute the principal DNA binding domain. Nuclear localization signals (NLS) are found within and just C-terminal to the DNA binding domain. The ligand binding domain makes up the bulk of the C-terminal half of the molecule, with the AF2 domain comprising the most C-terminal region. The AF2 domain is largely responsible for binding to co-activators such as the SRC family and DRIP (Mediator) in the presence of ligand. Regions on the second zinc finger and within the ligand binding domain facilitate heterodimerization with RXR. Corepressor binding is less well characterized but appears to overlap that of coactivators in helices 3 and 5, a region blocked by helix 12 in the presence of ligand.