Comparison of glucocorticoid-receptor complex binding to nuclei and DNA cellulose. Evidence for different forms of interaction.

Binding of dexamethasone . receptors with isolated nuclei, DNA-cellulose and cellulose has been compared with respect to dependence on salt concentration and resistance to KCl extraction and DNAse I digestion. A solution of cytoplasmic dexamethasone . receptor complexes was prepared by the incubation of rat thymus cells with steroid at 3 degrees C and breaking the cells by hypotonic lysis. Activation of the complexes was accomplished by warming the solution at 25 degrees C for 15 min. Activation significantly increased the ability of dexamethasone . receptors to bind to nuclei and DNA-cellulose but not to cellulose. Dexamethasone-receptor complexes bound to nuclei at 3 degrees C are completely resistant to extraction with 0.1 M KCl, 76% resistant to 0.2 M KCl and 20% resistant to 0.4 M KCl. Dexamethasone . receptors bound to DNA-cellulose are 45% resistant to extraction with 0.1 M and 0.2 M KCl and 29% resistant to 0.4 M KCl extraction. Cellulose-bound dexamethasone . receptors are not resistant to any of these extractions. DNAase I treatment releases 60% of the dexamethasone . receptors bound to DNA-cellulose but only 13% of those bound to nuclei, though at least 60% of the nuclear DNA is solubilized. The presence of 0.15 M KCl decreases binding of activated dexamethasone . receptors to nuclei by 73% but to DNA-cellulose by only 17%. Pretreatment of nuclei with 0.1--0.4 M KCl reduces their capacity to bind activated dexamethasone . receptors by 90% whereas similar treatment reduces the capacity of DNA-cellulose to bind dexamethasone . receptors by only 29%. Nuclei extracted with 0.1 M KCl appear to have a limited capacity to accept dexamethasone . receptors. These studies demonstrate that binding of dexamethasone . receptors to nuclei and DNA-cellulose differs by (a) the higher resistance of nuclear complexes to KCl and DNAase I treatment; (b) the much greater sensitivity of nuclei to KCl treatment.