Biochemical characterization and subunit structure of quail oviduct progesterone receptor

Abstract

The cytosolic quail oviduct progesterone receptor (PR) was studied under conditions that lead either to its stabilization or activation. Sedimentation coefficients and Stokes radii were respectively 7.8 ± 0.2 S and 7.6 ± 0.8 nm for the non transformed receptor (8S PR) and 3.9 ± 0.4S and 4.8 ± 0.6 nm for the transformed receptor (4S PR). The calculated molecular weight was 261 ± 29 KDa for the 8SPR and 83 ± 10KDa for the 4S PR. Density gradient centrifugation analyses showed that the monoclonal antibody BF4, directed against the 90 KDa hsp of the chick oviduct, cross-reacted with the quail 8S PR but not with the 4S PR. In contrast, polyclonal IgG-G6 antibodies, raised against the purified non transformed chick PR, cross-reacted with the non transformed as well as the transformed quail PR. The quail 8S PR was partially purified using NActac-Sepharose affinity chromatography and DEAE-Sephacel chromatography from cytosol prepared with protease inhibitors. The subunit structure of the purified quail and chick 8S PR were compared using SDS-PAGE, photoaffinity labeling and western immunoblotting. The quail PR was composed of two different proteins: a non-hormone binding protein (M r ∼ 90 KDa) which exhibited the same properties as the 90 KDa hsp protein of the chick oviduct and a single hormone binding subunit (M r ∼ 101 KDa). Based on its binding and immunological properties, this protein corresponded to the “B” form of the chick PR but was significantly smaller. In the quail cytosol or in purified PR preparations the “A” form of the PR was virtually absent; this observation is discussed.