Tissue specific binding in vitro of progesterone-receptor to the chromatins of chick tissues

When H³-progesterone is incubated with chick oviduct cytosol, it binds to a specific receptor protein. The subsequent binding of this complex to oviduct chromatin is greater than that of free progesterone alone. This specific affinity for the progesterone-receptor complex is not observed with spleen, heart, liver or erythrocyte chromatin. Progesterone incubated with the cytosols of non-target tissues such as liver or spleen shows no specific binding to chromatin from any source. Artificial complexes of chick histone and DNA display a low degree of non-specific binding. The results suggest that the chromatin of target tissue (oviduct) may contain "acceptor" sites for the hormone-receptor complex contained in the cytoplasm of the cell. The genome may thus be preprogrammed to receive the hormone receptor complex as it enters the nucleus of the target cell.