Purification of chick nuclear thyroid-hormone-receptor protein

A crude nuclear thyroid-hormone-receptor protein preparation from chick liver (an ammonium sulfate fractionation of high-ionic-strength-solubilized chromatin proteins) binds both triiodothyronine and thyroxine with high affinity. This crude preparation has characteristics similar to preparations from a variety of animal tissues, reported by several different laboratories, and is used for the further purification of the receptor protein. For this purification an affinity chromatography medium, 4-[N-(3,5,3'-triiodothyronine)-2-amino-3-hydroxypropoxy]-butylpropoxy -Sepharose ether, is used to take advantage of the observation that hydroxymercuribenzoic acid causes a reversible dissociation of the complex between triiodothyronine and the receptor protein. The hydroxymercuribenzoate treatment greatly increases this rate of dissociation at low temperatures compared with other methods, such as free triiodothyronine competition or an increase in ionic strength or pH. This procedure results a in purified fraction (1000-10000-fold with respect to binding triiodothyronine), which has a molecular mass of approximately 65 kDa and which retains a high degree of the original thyroid-hormone-binding activity.