The sex steroid hormones (estrogen and progesterone) stimulate growth, maturation and the development of new biochemical capacities in their reproductive target organs. These steroids play a major role in maternal physiology and fetal differentiation and their relationships to normal or oncogenic function of reproductive tissues are well established. Although steroid hormones exert major influences on the synthesis of nucleic acid and protein, the biochemical processes by which sex hormones regulate growth and function in target tissues are not yet defined in precise detail. The general objectives of our studies are to define the mechanism of action of reproductive steroid hormones and their receptors in regulating morphologic differentiation and biochemical specialization in target tissues. This will be accomplished by coordinating a network of investigations designed to uncover the mechanism by which steroid receptors interact with nuclear regulatory proteins (coactivators, adaptors, general transcription factors, chromatin modifiers, etc.) to effect regulation of target genes. We will emphasize experimental dissection of the protein-protein interactions which occur at the multiple ciselements inherent to eucaryotic genes. To understand steroid hormone action, we must understand the positive and negative regulation of receptor functional domains in context with the myriad of nuclear transcription factors to which they bind and through which they control transcription. Our studies will utilize the human progesterone receptor, but to establish regulatory concepts, we will carry out experiments using human estrogen, thyroid hormone, retinoic acid and orphan receptors. Cell-free binding and transcription approaches, technologies developed over the past 5 year period of this grant, will be a cornerstone of our methodology; all new concepts will be tested finally in the milieu of the intact cell. These studies will involve aspects of nucleic acid and protein biochemistry, protein purification, cell biology and molecular endocrinology. It is expected that the understanding derived from this project will be relevant to the biology of the natural reproductive hormones relative to maternal physiology, fetal development and the design of new contraceptive agents. The following proposed studies should also be pertinent to development of more precise theories for the biochemical mechanism of action of intracellular hormones and receptors in general.