JBC, Vol. 250, Issue 15, 6015-6021, Aug, 1975
Binding of glucocorticoid receptors to DNA
G. G. Rousseau, S. J. Higgins, J. D. Baxter, D. Gelfand and G. M. Tomkins
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.