The effects of steroid hormones are mediated by intracellular hormone-specific receptor proteins; the interaction between the hormone and its receptor increases the affinity of the receptor for nuclear binding sites, thereby modulating the expression of specific genes1. The glucocorticoid receptor is a soluble protein of relative molecular mass (M r) 94,000 (94K), present at a low relative abundance (≤0.01%); it has been purified to near-homogeneity2,3, and specific antisera and monoclonal antibodies have been produced4-6. Purified glucocorticoid receptor binds in vitro with high affinity to defined regions of DNA near regulated promoters7-10, and sequences essential for these interactions are functional in vivo as hormone-dependent transcriptional enhancer elements11,12. We have now cloned complementary DNA (cDNA) for the rat liver glucocorticoid receptor and we describe here a 2.6-kilobase (kb) receptor cDNA isolated following polysome immuno-enrichment of receptor messenger RNA with glucocorticoid receptor-specific antibodies. The receptor appears to be encoded by a single-copy gene which specifies a ∼6-kb transcript in rat and mouse cells; this mRNA is altered quantitatively and qualitatively in several mutant cell lines with specific defects in receptor function.
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