Oestrogen and progesterone receptors in chick oviduct chromatin after administration of oestradiol, progesterone or anti-oestrogen

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Abstract
Estrogen-primed and withdrawn chicks were injected with estradiol benzoate, progesterone, and/or the anti-estrogens tamoxifen and 4-hydroxytamoxifen. Estrogen receptors were studied in oviduct chromatin solubilized by mild digestion of purified nuclei with micrococcal nuclease. After a single injection of estradiol benzoate, ultracentrifugation on sucrose gradients of chromatin extracts labeled with [3H]-estradiol showed 2 peaks of estradiol binding sites, sedimenting at 13-14 S and 7-8 S. After repeated injections of estradiol benzoate, the 13-14 S peak increased more than the 7-8 S peak. After injection of anti-estrogen alone or together with estradiol benzoate, no [3H]estradiol-binding or 4-hydroxy[3H]tamoxifen-binding peaks were detected in the chromatin. Injection of progesterone also produced an increase of the 13-14 S and 7-8 S chromatin estradiol receptor. Progesterone receptor could only be detected in chromatin early after progesterone administration, and it sedimented in density gradients with the 12 S mononucleosome fraction. Tamoxifen injected together with progesterone gave higher levels of 13-14 S estrogen binding sites than did progesterone alone. The presence of a 13-14 S peak of estrogen binding sites in hormonal situations which promote a biological response in the chick oviduct, and the absence of this peak after administration of anti-estrogens, suggests that this subfraction of chromatin contains elements involved in gene regulation.