The functions of the group of proteins known as nuclear receptors will be understood fully
only when their working three-dimensional structures are known. These ligand-activated
transcription factors belong to the steroid-thyroid-retinoid receptor superfamily, which
include the receptors for steroids, thyroid hormone, vitamins A-and D-derived hormones,
and certain fatty acids. The majority of family members are homologous proteins for which
no ligand has been identified (the orphan receptors). Molecular cloning and …