A seasonal variation in the capacity of the progesterone-receptor complex to bind to isolated chromatin and partially purified acceptor protein bound to deoxyribonucleic acid (DNA) from the developed oviducts of estrogen-treated immature chicks has been described. Receptors isolated during the late winter fail to bind to these sites, whereas receptors isolated during the rest of the year show a marked binding. The level of binding to DNA remains unchanged throughout the year. A similar seasonal variation in the nuclear translocation in vivo of [3H] progesterone is demonstrated. Further, the effect of progesterone on the endogenous ribonucleic acid polymerase II (B) activity in vivo also displays a seasonal variation. The variations in the in vivo binding and transcriptional effects show a similar periodicity and timing as the in vitro binding. The level of one of the two molecular species of the progesterone-receptor complex is markedly reduced during the winter, thus explaining the overall decrease in receptor amounts during this same period. The receptor preparations isolated during the late winter-early spring show greatly reduced amounts of the “A” species as compared to those isolated during the other periods of the year. The ability of a particular receptor preparation to bind to the chromatin in vivo and in vitro or to the nuclear protein acceptor sites in vitro correlates with the level of the “A” receptor species. These data support the role of certain nonhistone protein-DNA complexes as acceptor sites for the progesterone receptor in the chick oviduct and that either the “A” receptor species or a combination of the “A” and “B” receptor species is required for nuclear binding of the progesterone-receptor complex.
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