Nuclear receptors represent a large class of ligand-activated transcriptional regulators; about 70 members of this protein family have been cloned from mammalian or insect species. Thus, it came as a great surprise when the recent completion of the Caenorhabditis elegans genome revealed at least 228 genes for nuclear receptors. Clearly, some of these receptors are homologues of known receptors, but most lack homologues in other species. Whether these receptors possess homologues in mammalian species is of great interest; if these do exist, the size of the nuclear receptor superfamily could also expand dramatically in humans. Copyright (C) 2000 Elsevier Science Ltd.
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