Estrogen Receptors as Nuclear Proteins
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The estrogen receptor appears to be a nuclear protein regardless of whether or not it is occupied by an estrogenic ligand (1). As illustrated in Figure 1, the estrogen receptor is thought to be bound with low affinity to some nuclear component. Thus the unoccupied receptor is not in a soluble form in the intact nucleus but is readily extracted into dilute aqueous buffers upon homogenization. When receptor-containing cells or tissues are exposed to estrogens, the estrogen-receptor complex undergoes a conformational change resulting in an increased affinity for nuclear components. Therefore the estrogen-receptor complex can be extracted only with buffers containing high salt concentrations (0.4 M NaC1). We believe that the estrogen-induced conformational change is the critical event in estrogen action.
KeywordsEstrogen Receptor Glucocorticoid Receptor Nuclear Matrix Growth Hormone Gene Steroid Hormone Action
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