1. 1. Previous studies have demonstrated that progesterone, complexed with the oviduct receptor protein, is extensively bound by the deoxyribonucleoproteins (chromatin) of the mature chick oviduct. The chromatin of other tissues of the chick did not display this extensive binding. Results of studies presented here show that the progesterone receptor complex is extensively bound by the chromatin of the chick oviduct at all stages of development. 2. 2. Analyses of the chromatins indicate that the levels of nonhistone (acidic) protein and RNA as well as the ability of the chromatins to serve as a template for DNA-dependent RNA synthesis are altered in a specific pattern during differentiation of the chick oviduct. Differences in the levels of histones were less and showed no specific pattern. The capacity of the oviduct chromatins to bind the progesterone-receptor complex also varies throughout the development of the oviduct. The extent of binding the hormone receptor complex appears to be correlated with the levels of acidic proteins and RNA of the oviduct chromatins. 3. 3. Since chromatin of the undifferentiated oviduct binds the progesterone-receptor complex more extensively than the chromatins of other tissues, e.g., spleen or erythrocyte, it is speculated that the hormone binding capacity is not established during the estrogen induced maturation of the oviduct but must be established earlier at some stage of organogenesis of the chick oviduct.
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