There are actually three retinoid X receptors (RXR), RXR-alpha, RXR-beta, and RXR-gamma. The RXR's are nuclear hormone receptors with activity similar to that seen in other steroid receptors such as estrogen or progesterone but more similar in form to PPAR, LXR and FXR. 9-cis retinoic acid is the natural ligand for RXR and like other steroid receptors, when activated, it translocates to the cell nucleus, forms a dimer (in this case a heterodimer) and binds to hormone response elements on DNA which elicits expression or transrepression of gene products. The RXR's are also known to act as promiscuous heterodimer partners for the non-classical steroid receptors (classical steroid receptors are androgen, estrogen, glucocorticoid, progesterone and mineralocorticoid).