Progesterone-binding Components of Chick Oviduct

Abstract

Abstract Specific progesterone-binding components are shown to be present in oviduct nuclei of estrogen-treated chicks. The macromolecular complex containing 3H-progesterone can be detected by sucrose gradient centrifugation and distinguished from chick plasma transcortin by Agarose gel filtration. The nuclear binding components behave identically to the cytoplasmic components previously described in our ultracentrifugal, chromatographic, and inactivation studies. The macromolecular-progesterone complex formed in vivo or in vitro can be extracted from nuclei by 0.3 m KCl. Little or no salt-extractable progesterone-binding activity can be detected in oviduct nuclei prior to progesterone administration. The binding molecules appear to exist initially in oviduct cytoplasm, where they presumably function as specific target tissue receptors. Following injection of 3H-progesterone in vivo or incubation of oviduct slices in vitro with 3H-progesterone, a progressive increase in nuclear binding occurs. The data indicate an absolute prerequisite for an initial interaction of the steroid with the cytoplasm, and a concomitant depletion of cytoplasmic receptor as nuclear binding increases. These results, and the apparent identity of the cytoplasmic and nuclear components, support the hypothesis that the nuclear macromolecular-steroid complex arises by a hormone-dependent transfer of the cytoplasmic receptor complex into the nucleus.