Interaction of 3H-dexamethasone-receptor complex with nuclei: inhibition by Ethidium Bromide

Several binding characteristics of the Dexamethasone (DEX)-receptor complex(RC) to nuclei from rat tissues were examined in the presence of Ethidium Bromide(EB). In the cell-free experiments, EB partially prevented the binding of the liver DEX-RC to nuclei and two kinds of nuclear binding of the DEX-RC, one was sensitive and the other was resistant to EB, were observed. In addition, the EB-resistant nuclear binding that showed a high-affinity and low-capacity nature was observed only in the bindings of the 3H-DEX-RC to nuclei derived from the liver of fetal and adult rats and the thymus of adult rats. The bindings of 3H-5 alpha-Dihydrotestosterone(DHT)-RC and 3H-17 beta-Estradiol(E2)-RC to liver nuclei exhibited low-affinity and non-saturation even in the presence of EB. Furthermore, it was revealed, that the EB-resistant sites of the nuclear binding were for the "DNA-unbound" form of 3H-DEX-RC, while the RC of "DNA-bound" form was bound to the EB-sensitive sites.