[Localization of (3H)hydrocortisone in rat liver nuclei]

The content of hydrocortisone in rat liver nuclei reaches its maximum in 1 hour after its intravenous injection and remains stable for another hour. In three hours after introduction it falls to the initial level (15 min after the injection of [3H]hydrocortisone). The accumulation of the hormone in nuclei completely coincides with kinetics of reversible DNA supermethylation and correlates with the induction of transcription. No free [3H]hydrocortisone was found in nuclei, in isolated nuclei it is found in the fraction of nuclear membranes, nucleoplasma, nucleolus and chromatin. Specific radioactivity of [3H]hydrocortisone (d. p. m. per 1 mg of DNA) in active chromatin is 10--50-fold as high as in condensed chromatin and is 10--15-fold as high as in nucleolus. It is suggested that there are at least two types of binding hormonereceptor complexes with chromatin. The initial binding of these complexes with condensed chromatin may result in its structural rearrangement (euchromatization), in the appearance of more specific secondary sites for binding hormone-receptor complexes with chromatin DNA, and also in the appearance of methylation and transcription initiation sites in DNA.