| Organization of the steroid receptor molecule
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| Steroid receptors are products of a gene family with important similarities
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| One central feature of all the steroid receptor proteins is the similarity in organization of their receptor molecules. Each receptor has a DNA-binding domain, a transcription-activating domain, a steroid-hormone-binding domain, and a dimerization domain. There are three striking features about the structure of the steroid hormone receptors:
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- The DNA-binding region always contains a highly conserved zinc finger region, which, if mutated, results in loss of function of the receptor;
- The DNA-binding regions of all the steroid hormone receptors have a high degree of homology to one another;
- The steroid-binding regions show a high degree of homology to one another.
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| These common features have identified the steroid receptor proteins as products of a gene family. It would appear that, during the course of evolution, diversification of organisms has resulted in the need for different steroids with varied biological actions and, consequently, a single ancestral gene has undergone duplication and evolutionary change over millions of years, resulting in a group of related, but different receptors (Fig. 33.6).
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