There are actually three retinoic acid receptors (RAR), RAR-alpha, RAR-beta, and RAR-gamma with each receptor having two, four and two splice variants respectively. The RAR'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. All-trans retinoic acid is the natural ligand for RAR 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. 9-cis retinoic acid is the natural ligand of another nuclear hormone receptor termed the retinoid x receptor.