Nuclear-hormone mediated changes in chromatin solubility.

Rat liver nuclei were incubated with either thyroid hormone or angiotensin (AII) at varying concentrations or with buffer (control) prior to digestion with micrococcal nuclease. Concentrations of hormones greater than 10(-10)M were effective in increasing the solubilization of chromatin with physiological levels (10(-9)M) of AII showing an approximate 2.4 fold increase over control. Nuclei were also isolated from animals treated in-vivo with either AII or buffer (control) and chromatin solubility was increased in the AII treated nuclei even prior to the addition of exogenous nuclease, presumably from the action of endogenous nucleases. The data suggest that hormone-induced increases in solubility are a reflection of structural changes in chromatin which enhance the accessibility of DNA to endonuclease attack.