Estrogen-related receptor alpha (ERR alpha) is an orphan member of the superfamily of nuclear hormone receptors. ERR alpha was initially isolated based on its sequence homology to the estrogen receptor but is not activated by classic estrogens. Binding site selection experiments show that ERR alpha preferentially binds to an ERR alpha response element (ERRE) containing a single consensus half-site, TNAAGGTCA. Data demonstrate that 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 (1). The estrogen-related receptors ERRalpha and ERRbeta (formerly ERR1 and ERR2) form a subgroup of the steroid/thyroid/retinoid receptor family. ERRalpha and ERRbeta are homologous to the estrogen receptor and bind similar DNA targets; however, they are unable to activate gene transcription in response to estrogens (2).
