Project Summary The overarching goal of this competing renewal grant is the elucidation of signaling pathways and the mechanisms by which cells elicit selective responses to changes in their environment. Intracellular signaling pathways, such as inositol phosphate (IP) messengers, are key regulators of biology and inborn errors in IP networks result in disease. Over eighty genes are dedicated to the synthesis and breakdown of IP messengers. While much is know about IP metabolism, less information is available as to how the ensemble of dozens of IP molecules are decoded: that is, what are the receptors and how does IP binding alter their function? Our laboratory has developed a new method for identifying decoders of IP signals and has made a key discovery that inositol hexakisphosphate (IP6) is a structurally bound component and regulator of several members of the ancient family of N-terminal acetyltransferases, known as NATs. The focus of this proposal is to rigorously define the mechanisms by which IP6 and other metabolites influence NAT structure and function, and ultimately alter protein N-terminal acetylation in normal and disease cellular states. The work outlined in this proposal will contribute fundamental insights into how cells use lipid-derived inositol messengers to enhance regulation, specificity and complexity of signaling biology.