PURIFICATION AND CHARACTERIZATION OF THE CHICK OVIDUCT PROGESTERONE RECEPTOR A SUBUNIT

The DNA-binding A subunit of the chick oviduct progesterone receptor has been purified approximately 20,000-fold to apparent homogeneity. The procedure employs phosphocellulose, DNA-cellulose and DEAE-cellulose column chromatography. Purity has been assessed by polyacrylamide gel electrophoresis in two denaturing systems. The protein is obtained with about 20% of the available ligand sites complexed with labeled progesterone. Dissociation kinetics and displacement studies show the protein is identical to the crude starting material. Molecular weight (Mr) determined by gel electrophoresis in l% Na dodecyl SO4 is 79,000. Values for Stokes radius (46 Å) and sedimentation coefficient (3.6 S) are in agreement with the properties of the crude A protein and give an indicated molecular weight of 72,000 for the native protein. The purified protein retains its DNA-binding ability to both DNA cellulose columns and to free DNA using a nitrocellulose filter adsorption assay. The latter assay shows no saturability nor DNA sequence specificity under the conditions employed. The binding is enhanced 8-fold by heat denaturing the DNA. © 1979.