ABSTRACT
In this chapter, the authors describe the progress that has been made in characterizing the avian progesterone receptor. They argue that phosphorylation of the progesterone receptor is a significant event relating to hormone action. Protein component problem was later resolved by a more thorough analysis of the purified receptors. Before phosphorylation sites on the progesterone receptor could be investigated, it was necessary to obtain the receptor in a highly purified state. From antibodies properties, it was later identified as one of the major heat shock proteins, heat shock protein 90 (hsp 90). Panels A and B represent the A and B receptor components, respectively. Both appear to be phosphorylated at multiple sites. Whether treatment caused loss in receptor occurs in relation to nuclear events or as an independent process is not known. The progesterone treatment causes a very marked and rapid increase in receptor phosphorylation.
