Binding of glucocorticoid receptors to DNA

DNA has been implicated as the nuclear acceptor for receptor-glucocorticoid complexes. The present study concerns the interaction of these complexes, isolated from cultured rat hepatoma cells, with purified DNA. This association is rapid, reaching a maximum within a few minutes at 0 degrees, whereas dissociation requires several hours. DNA binds neither free glucocorticoids nor those complexed with transcortin or cytosol proteins different from the receptor. Receptors which are not complexed by steroid have little or no affinity for DNA. "Activation," necessary for the binding of receptor-steroid complexes to isolated nuclei, also enhances DNA binding. The capacity of DNA for binding receptor-steroid complexes is large; saturation was not observed at the complex concentrations studied, using either crude or partially purified receptor preparations. The association of complexes with DNA is inhibited by divalent cations, at increasing ionic strengths, and by mercurial reagents. Complexes bind equally well to bacterial, bacteriophage, or rat DNA; however, there was either no or substantially reduced binding by bacterial 23 S rRNA. The binding of complexes to native DNA is roughly 3-fold greater than to denatured DNA. These characteristics are consistent with the possibility that DNA is the nuclear acceptor for receptor-glucocorticoid complexes; however, the actual composition of the acceptor sites remains unknown.