Isolation of a chromatin fraction from calf endometrium highly enriched in estradiol binding sites

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Abstract
The intranuclear distribution of [3H]-estradiol binding sites was studied in highly purified nuclei isolated from calf endometrial tissue pre-incubated with the labeled hormone. The major part(˜85%) of the receptor bound estradiol was found associated with the extranucleolar chromatin; only a negligible amount of [3H]-estradiol (˜8%) sedimented with the nu-cleolar fraction.[3H]-estradlol labeled chromatin was then fragmented by sonication and fractionated by sucrose density gradient sedimentation under different conditions of centrifugation. The vast majority of the [3H]-estradiol was invariably found to be associated with a fast sedimen-ting fraction which contained only 5 to 10% of the nuclear DNA. The concentration of estradlol receptors (per weight of DNA) in this fraction was 25- to 50-fold higher than that found in the slow sedimenting major chromatin component. Chemical analysis showed this fraction to have a high protein/DNA ratio but no phospholipids were detected.