Characterization of nuclear estradiol receptors released by micrococcal nuclease and deoxyribonuclease I

Interaction of estradiol receptor with chromatin was probed by nuclease digestion of receptor-chromatin complex. The complex was formed by incubating partially purified receptor with chromatin. Micrococcal nuclease digestion of the complex released a 7S form of receptor which could be converted to 2.8S form by DNAase I. Digestion of the complex with DNAase I yielded different forms of receptors ranging from 7S to 2.8S depending on the digestion time. Receptor distribution was also examined by isolating nuclei form tissue pre-incubated with radioactive estradiol. Micrococcal nuclease digestion of receptor-filled nuclei released 7S, 5.5S and 3.5S forms of receptors. Collectively, these results indicate that the 7S nuclear receptor may have an associated chromatin fragment which is sensitive to DNAase I activity. The desirable features of receptor-chromatin method over conventional methods for studies relating to receptor interaction at the gene site are discussed.