Non-activated Form of the Progesterone Receptor in the Chick Oviduct

According to current ideas, in order to exert their biological effects, steroid hormones must first bind to their cytoplasmic receptors, and the complex then moves into the nucleus of the target cell. The process by which the receptor-hormone complex acquires the ability to bind to nuclei and to polyanions, such as DNA, is termed “activation”, the mechanism of which is unknown. It is important to clarify what structural changes in the receptor accompany the activation process, for a better understanding of both activation itself, and the mechanism of hormone action as a whole. Our approach to this problem has been to study the physical and biological properties of the progesterone receptor before and after activation has occurred.