Progesterone-binding Components of Chick Oviduct: V. EXCHANGE OF PROGESTERONE-BINDING CAPACITY FROM TARGET TO NONTARGET TISSUE CHROMATINS

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Abstract Progesterone, when forming a complex with a specific protein receptor molecule, interacts in vitro with intact chick oviduct chromatin. In the present study, a series of experiments was performed to elucidate the nature of the chromatin sites of oviduct responsible for binding the progesterone receptor. The proteins of chromatin from various chick tissues were dissociated from DNA and reconstituted back to the DNA of either the same or different tissue. The chemical analysis and polyacrylamide gel electrophoresis demonstrate that the histones are quantitatively reintegrated into the chromatin without detectable degradation when protease inhibitors are present during the reconstitution. Comparison of the chemical composition and immunochemical analysis of the untreated and reconstituted chromatins indicates that non-histone (acidic) proteins also can be switched from oviduct chromatin to the DNA of other tissues to form chromatins. The transfer of the acidic proteins from the chromatin of one tissue to that of another results in a corresponding exchange of the template capacity so that the hybrid chromatin resembles the chromatin serving as the source of the acidic proteins. These data suggest that the acidic proteins are involved in maintaining open template. Reconstituted chick oviduct chromatin maintains the capacity to bind the progesterone-receptor complex. This tissue-specific binding is transferred to chromatins of non-target organs by exchanging the acidic chromatin proteins during reconstitution. Moreover, quantitative microcomplement fixation assays using antisera specific for the oviduct DNA-acidic protein complex indicate that the conformation of acidic proteins following transfer is similar to that found in the native oviduct chromatin. A subfraction of the acidic proteins of oviduct chromatin has been found to contain the acceptor molecules which are responsible for the binding with the progesterone-receptor complex. These tissue-specific acceptor proteins thus appear to be the molecules responsible for the binding of progesterone-receptor complex to oviduct chromatin.