A long term objective of our research effort is to define factors that influence the specificity and efficiency of signal processing by heterotrimeric G-proteins. Accessory proteins provide alternative modes of signal input to G-protein signaling systems and/ or segregate a signaling complex to microdomains of the cell, regulate the basal activity, efficiency and/or specificity of signal transfer. Our goals are to define such accessory proteins, their mechanism of regulation and their role in various diseases. One such group of accessory proteins is defined by the family of Activators of G-protein signaling or AGS proteins discovered in a yeast-based functional screen for receptor-independent activators of G-protein signaling. This proposal focuses on AGS3 and related Group II AGS proteins. SPECIFIC AIM #1 Identify mechanisms regulating the interaction of AGS3 with G-proteins. SPECIFIC AIM #2 Define the functional impact of a loss of AGS3 in the intact animal. SPECIFIC AIM #3 Identify and characterize additional disease- or adaptation-specific AGS proteins using a yeast-based functional screen for receptor independent activators of G116, Gs1, Gi12, and Gi13. AGS3 and related accessory proteins provide unexpected mechanisms for regulation of the G-protein activation cycle and have opened up a new area of research related to the cellular role of G-proteins as signal transducers. The concepts advanced with their discovery provide unexpected avenues for therapeutics and understanding disease mechanisms. PUBLIC HEALTH RELEVANCE: The work proposed in this application focuses on basic mechanisms for regulation of a major system that controls function of various tissues in the body including brain, heart and adipose. The area of investigation has merit from the perspective of disease diagnostics and the development of new therapeutic strategies.