The selective isolation of the uterine oestradiol-receptor complex by binding to oligo(dT)-cellulose. The mediation of an essential activator in the transformation of cytosol receptor

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Abstract
The [3H]estradiol-receptor complex was selectively isolated from rat uterus cytosol by column chromatography on oligo(dT)-cellulose. Optimal conditions are described for the binding of the complex to oligo(dT)-cellulose, which is similar to its binding to DNA-cellulose. The cytosol complex has an apparent MW of 50,000-60,000 in high salt concentrations, as determined by Sephadex G-100 chromatography. This corresponds to the 4S cytoplasmic estradiol receptor. In binding to oligo(dT)-cellulose, the receptor is transformed into a form with an apparent MW of 100,000-120,000, corresponding to the 5S nuclear receptor complex. This transformation mimics the conversion in vivo of the cytoplasmic estradiol receptor into the nuclear form. The binding of the complex to oligo(dT)-cellulose as a 5S nuclear form requires the mediation of an activating factor present in the cytosol. This requirement for an activating factor is discussed in relation to reports that nuclear binding of the estradiol-receptor complex is not dictated solely by the availability of the cytoplasmic estradiol receptor.