George Pikler

Role of nuclear proteins as high affinity sites (“acceptors”) for progesterone in the avian oviduct

Abstract Administering multiple doses of progesterone to immature chicks results in the detection of several classes of oviduct nuclear binding sites. Comparisons of serum progesterone levels and responses to RNA polymerase I and II activities with the nuclear binding, indicate that the highest affinity classes of sites are the biologically important ones. In vitro binding studies using isolated progesterone receptor complex also reveal the presence of these multiple classes of sites. The highest affinity class of nuclear sites in the oviduct, representing 6000 to 10,000 sites per cell with a K D ~ 10 −9 M, appear to be tissue specific. These sites are present but completely masked in the chromatin of non-target organs (spleen and erythrocyte), while 70% are masked in the target tissue (oviduct). Further fractionation studies involving DNA affinity chromatography using chromatin-cellulose resins and molecular sieve-chromatography using Agarose-GuHCl resins reveal that the “acceptor” activity is associated with two molecular weight-proteins between 12,000 and 17,000. These proteins are bound with very high affinity to DNA. The “acceptor-proteins” must be reannealed to DNA to achieve binding activity. These results support that acidic proteins determine the high affinity nuclear binding sites for steroids.

Isolation and characterization of the nuclear acceptor that binds the progesterone-receptor complex in hen oviduct.

Progesterone binds to the nuclear chromatin of hen oviduct cells within minutes after its administration. This is followed by alterations in the RNA polymerase activities (15–30 min after treatment) and the appearance of specific messenger RNA (2 hr after treatment). It appears that the first nuclear event resulting in changes in gene expression represents the chromatin binding. Further characterization of this nuclear interaction, involving the administration of multiple doses of progesterone to estrogen‐treated immature chicks, revealed the presence of several classes of nuclear binding sites in the oviduct. Comparisons of serum progesterone levels and responses of RNA polymerase I and II activities with the nuclear binding indicated that the highest‐affinity classes of sites (∼ 10,000 sites per cell) are the biologically important ones. Binding studies in vitro, using isolated progesterone‐receptor complex, also reveal the presence of these multiple classes of sites. The highest‐affinity class of nucle...