Steroid hormone receptors have attachment site forall except:
Correct Answer: Transcription repressors
Description: Transcription repressors Steroid hormone receptors are intracellular receptors that perform signal transduction for steroid hormones. Steroid hormone receptors are pa of the nuclear receptor family that also includes a group of homologous structured receptors that bind to non-steroid ligands such as thyroid hormones and vitamin A, as well as to vitamin D. All these receptors are transcription factors. They act on nuclear DNA to regulate gene transcription. The steroid hormones, thyroid hormones, retinoic acid form pa of Group I hormones. Group 1 hormones are those which act on intracellular receptors whereas Group II hormones act on receptors located on the extracellular surface of the plasma membrane. Group I hormones activate gene transcription by 2 different mechanisms. Steroid hormone receptors are located within cytoplasm, in complex with heat shock protein (HSP). The steroid hormones being lipophilic readily diffuse through the plasma membrane and bind to the steroid receptors. Ligand binding causes dissociation of the heat shock protein from the receptor. The receptor ligand complex then moves into the nucleus and bind with high affinity to a specific DNA sequence called the hormone response element (HRE). This DNA-bound, liganded receptor serves as a high-affinity binding site for one or more transcription activator proteins. This complex then activates gene transcription. In contrast to steroid receptors, receptors for thyroid hormones and retinoids lie within the nucleus already bound to the Hormone response element. However this DNA-bound receptor fails to activate transcription because its complexed with a transcription repressor. This receptor-corepressor complex serves as an active repressor of gene transcription. Binding of thyroid or retionoid hormone results in dissociation of the transcription repressor from the receptor. Receptor activators then bind to the DNA bound liganded receptor complex to activate gene transcription.
Category:
Physiology
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