Retinoic acid receptors are located in the nucleus and commonly form complexes with steroid hormone receptors in order to regulate the production of essential gene products. Retinoic acid receptors bind corepressors in the absence of their ligand, retinoic acid, which is formed from the metabolism of vitamin A. Retinoid X receptors are activated by binding to 9-"cis"-retinoic acid, a specific isomer of retinoic acid. Other retinoic acid receptors are less specific, allowing them to bind isomers of retinoic acid with similar affinities.