Transformation and phosphorylation of purified molybdate-stabilized chicken oviduct progesterone receptor

The non-transformed, molybdate-stabilized chick oviduct cytosol progesterone receptor was purified approx. 7000-fold using biospecific affinity resin (NADAC-Sepharose), DEAE-Sephacel chromatography and gel filtration on Bio-Gel A-0.5m agarose. The purified preparation contained progesterone receptor which sedimented as a 7.9S molecule, had a Stokes' radius of 7.5 nm, was composed of three major peptides corresponding to Mr 108,000, 90,000 and 79,000. Upon removal of molybdate, the purified [3H]progesterone-receptor complex could be transformed from the 8S form to a 4S form by exposure to 23 degrees C or by an incubation with 10 mM ATP at 0 degrees C. The purified thermally transformed receptor could be adsorbed to columns of ATP-Sepharose. No cytosol factor(s) appeared to be required for the 8S to 4S transformation of purified receptor or for its subsequent binding to ATP-Sepharose. Incubation of purified non-transformed receptor preparation with [gamma-32P]ATP and cAMP-dependent protein kinase led to incorporation of radioactivity in all the three major peptides at serine residues. The results of this study show for the first time that purified 8S progesterone receptor can be phosphorylated in vitro by a cAMP-dependent protein kinase, and that it can be transformed to a 4S form by 0 degrees C incubation with 10 mM ATP.