The effect of partially purified dexamethasone receptor on RNA synthesis in rat thymus and liver nuclei.

DEAE Sephadex-A-50 chromatography of rat liver and thymus cytosol charged with dexamethasone (0.1 microM) and heated at 25 degrees C for 30 min, separates two main hormone--receptor complexes, one in the flow through (DE-1) and one eluting with 150 mM [Cl-] (DE-2). Incubation of these two fractions with homologous nuclei results in a 20% stimulation and a 20-25% inhibition of transcription of liver and thymus nuclei, respectively. No difference was observed between the action of DE-1 and DE-2. If the DE-1 and DE-2 fractions of cytosol charged with the glucocorticoid antagonist, cortexolone, are used under the same experimental conditions, no effect on the transcriptional activity of liver or thymus nuclei can be observed. The fact that from nuclei only DE-1 can be isolated, not DE-2, suggests that DE-1 is the intranuclearly active form and that DE-2, with a still unknown mechanism, is transformed to DE-1. A linear relation exists between the number of GR-complexes (DE-1 or DE-2) translocated and the change in RNA synthesis. Transcriptional effects start when a critical number of acceptor sites are occupied in the nucleus (approximately 200-300 sites/nucleus) for both receptor forms.