Estrogen-related receptor alpha (ERR alpha) is an orphan member of the superfamily of nuclear hormone receptors. It was initially isolated based on its sequence homology to the estrogen receptor but is not activated by classic estrogens. ERR alpha preferentially binds to an ERR alpha response element (ERRE) containing a single consensus half-site, TNAAGGTCA. ERR alpha can control the expression of MCAD through the NRRE-1 and thus may play an important role in regulating cellular energy balance in vivo.