Studies with chymotrypsin and RNAase showing a heterooligomeric structure of the glucocorticoid receptor complex from rat liver which is stabilized by a low molecular weight factor.

The glucocorticoid receptor from rat liver displays a differential sensitivity toward digestion by chymotrypsin and RNAase A that is dependent on its activation state. Unactivated (9-10 S) receptor is not digested by these enzymes, while activated 7-8 S receptor is. Chymotrypsin treatment yields an approx. 3 S form, while RNAase treatment yields a 4.9 S form that is distinct from the high-salt 4 S form. To firmly establish that the results are due to specific hydrolytic activities of the particular enzymes, we show that the chymotrypsin effect is inhibited by diisopropylfluorophosphate and not RNAasin, while the reverse is true for RNAase A. We further show that the differential sensitivity toward chymotrypsin is due to the association of a proteinase-resistant, heat-stable low molecular weight factor with the unactivated glucocorticoid receptor. When this factor is removed by warming, dialysis or molecular sieving of the receptor complex, the complex becomes sensitive to chymotrypsin. We also show that moderate chymotrypsin treatment yields a 6-7 S form of the receptor which is composed of, at least, RNA and the 4 S receptor. On the basis of these results, we propose that the 9-10 S receptor is composed of a low molecular weight stabilizing factor whose presence apparently alters the conformation of the complex such that the RNA and the RNA-binding site of the receptor are protected, a chymotrypsin-sensitive factor, RNA and the 4 S receptor itself.