Purified glucocorticoid-receptor complexes from rat liver cytosol preferentially bind in vitro to a homologous DNA fraction whose transcription is activated by cortisol.

The in vitro binding of 2000-fold purified rat liver glucocorticoid-receptor complexes to functionally differing homologous DNA fractions has been studied. The effectiveness of receptor binding to the transcriptionally active DNA, isolated from rat liver 4 h after cortisol administration, increased by 1.6-1.8-fold with simultaneous reduction in receptor affinity for the hardly extractable DNA fraction. The analogous DNA fractions from control animals did not differ in ability to bind the receptor. This suggests that sites of high affinity for the receptor are directly involved in the in vivo process of hormonal transcription activation.