The long term objectives of this project are to understand metazoan transcriptional regulation, and mechanisms by which a regulatory factor can specify different programs of gene expression as a function of developmental or physiological cues. The general strategy of the proposed research is to analyze regulation by members of the intracellular receptor (IR) superfamily, which includes receptors for steroids, thyroid hormone, retinoids, and other small lipophilic ligands. Combinatorial regulation likely reflects the controlled assembly of multifactor regulatory complexes, whose components and functions are context-dependent. Thus, the assembly and functions of IR regulatory complexes in different contexts will be dissected mechanistically, in settings ranging from pure proteins to whole organisms. The specific aims of the present study are to characterize the structure and activities of IR regulatory complexes under conditions in which the ligand (which defines a cell-specific context) or the response element (which defines a gene-specific context) are varied within the complexes. Four goals are envisioned: (1) determine how functionally distinct regulatory complexes are specified by ligands; (2) determine how gene-specific regulatory complexes and IR functions are specified by response elements; (3) determine the structure and significance of receptor interactions with Swi/Snf chromatin remodeling complexes; (4) investigate IR regulatory complex formation and function in the simple metazoan C. elegans. In these experiments, molecular genetic, biochemical and structural approaches will be used to identify functional surfaces and interacting factors that specify transcriptional activation, repression, composite regulation and synergy in vitro, in cells and in whole animals. IRs have been implicated in a wide range of diseases, including cancer, hypertension and inflammation, and IR ligands are widely used as therapeutics, diagnostics and chemopreventatives. Thus, understanding the principles and mechanisms of IR action has important implications for health, and for detecting, treating and curing disease.