ABSTRACT
The rabbit progesterone receptor undergoes two phosphorylation reactions, a basal phosphorylation and a second hormone-regulated reaction. The role of the hormone-regulated phosphorylation is not at present understood. It may be a necessary step in the regulatory action of receptor on gene transcription. However, binding of the receptor to specific regions of the uteroglobin gene was no different, whether the receptor had undergone hormone-dependent phosphorylation or not. The possibility remains that hormone-dependent receptor phosphorylation plays a role in reactions that follow receptor binding to the gene, and which probably involve interaction with the transcriptional machinery. The group of hormones consists of molecules which act mainly at the level of the cell nucleus, regulating the transcription of specific genes. It has been proposed, using the chick oviduct receptor as a model, that the progesterone receptor is an oligomer formed by equal amounts of two steroid-binding subunits.
