Properties of the partially purified activated glucocorticoid receptor of rat liver. Binding to chromatin subunits

The activated glucocorticoid receptor from rat liver has been purified over 3000-fold by repeated adsorption to phosphocellulose. The partially purified receptor-triamcinolone complex is stable for sever weeks at -75 degrees C in the presence of 0.1% bovine serum albumin, and sediments at 2.9 (+/- 0.1) S in sucrose gradients containing 0.15 M Na Cl. The Stokes' radius of the partially purified receptor is 26.5 A, and the frictional ratio is 1.14, indicating that at near physiological salt concentration the activated receptor is slightly elongated and has a molecular weight of 33 500. These preparations of receptor are free of exo- and endonucleases and bind to DNA and chromatin, as well as to the native chromatin subunits, the nucleosomes. Removal of histone H1 and further digestion of the nucleosomal DNA to the core size of about 140 base pairs indicate that the integrity of the nucleosome structure determines the extent of interaction with the glucocorticoid receptor. Although the binding of receptor to unfractionated rat liver chromatin is more efficient than to chicken erythrocyte chromatin, the nucleosomes of both tissues bind equal amounts of receptor. Therefore, the factors responsible for this tissue difference do not reside in the nucleosomes, but rather in a higher order structure of the chromatin or in that part of the genome which is not organized as nucleosomes.