Project summary The presence of dsDNA in the cytoplasm signals serious problems in eukaryotic cells, ranging from dysfunctional mitochondria to pathogen invasion. In mammals, the innate immune system detects these rogue dsDNA and initiate inflammatory responses. Cytoplasmic dsDNA sensing pathways are integral to host defense against numerous pathogens, and their malfunctions are also implicated in various human maladies. Here, we will define the molecular mechanisms by which cytoplasmic dsDNA sensors initiate host innate immune responses in a coordinated fashion. In Aim 1, we will resolve several controversies regarding the activation mechanism of cGAS such as why dsDNA length matters (or not), what the role of N-domain is, and how cGAS dimerizes on dsDNA. In Aim 2, we will resolve a fundamental mechanistic question in innate immunology as to what defines the dsDNA specificity of cGAS, AIM2, and IFI16. We will then test whether cellular RNA can act as a buffer to minimize the spurious activation of these sensors. In Aim 3, we will determine whether differential kinetics of cGAS, AIM2, IFI16, and the TREX1 nuclease can shape the overall host response against cytoplasmic dsDNA. We will then investigate agonism and antagonism among these sensors in generating well-balanced host responses against cytoplasmic dsDNA.