To further understand the structure-function relationships of the chicken oviduct progesterone receptor, the effects of in vivo and in situ progesterone treatment were studied. Immunoprecipitated receptors isolated from oviduct slices incubated in the presence of H332PO4 exhibited hormone-dependent phosphorylation. This was correlated with an increase in the apparent mol wt of receptors when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and increased DNA binding of total cytosolic receptors. Further, in vivo progesterone treatment resulted in dissociation of both the A and B receptor forms from nonhormone-binding proteins (such as heat shock protein-90) in vitro when analyzed by sucrose gradient ultracentrifugation. The 4S and 8S receptors were separated by phosphocellulose column chromatography, treated with ammonium sulfate to convert all receptors to DNA-binding forms, and analyzed for binding to DNA cellulose. The 4S receptor produced as a consequence of in vivo hormone treatment had a 3.35-fold higher affinity for DNA and bound to about a 3-fold greater extent than receptor that did not show altered interaction with other proteins. Thus, in vivo progesterone treatment results in increased receptor phosphorylation, altered interaction with heat shock protein-90, and increased DNA binding.
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