Understanding host-viral interaction is an essential step in developing safe and effective antimicrobials against biodefense agents and emerging pathogens. Early detection of invading viruses by the host depends on a limited number of specific intracellular receptors that detect viral patterns and activate signal transduction cascades, thereby triggering interferon (IFN)-mediated anti-viral defense mechanisms. Retinoic acid-inducible gene I (RIG-I) has emerged as a key cytosolic viral RNA receptor for sensing emerging viruses, including the influenza virus and hepatitis virus C (HCV). In addition, members of the tripartite motif (TRIM) protein family, containing a RING-finger domain, B box/coiled-coil domain (B Box/CCD), and a SPRY domain, play a major role in the inhibition of the lifecycles of viruses. Furthermore, the interconnection between the RIG-I and TRIM family is required to initiate the induction of the protective IFN-mediated host anti-viral innate immunity. Our collaborative works have demonstrated that the RIG-Imediated IFN pathway requires multiple step processes: upon viral infection, the C-terminal "regulatory" domain (RD) of RIG-I recognizes viral RNA in a 5'-triphosphate-dependent manner, leading to RIG-I dimerization and ATPase activity. Subsequently, RIG-I undergo a robust ubiquitination induced by the TRIM25 E3 ligase, enabling RIG-I to interact with the downstream CARD-containing mitochondrial anti-viral signaling (MAVS) protein and thereby inducing antiviral signal transduction to limit viral replication and transmission. The goal of this study focuses on better understanding the regulation of RIG-I and TRIM25 pathways: how posttranslational modifications affect RIG-I and TRIM25 signaling activity (Aim 1), what the modes of feedback regulation for the RIG-I and TRIM25 pathways are (Aim 2), and finally, what roles RIG-I and TRIM25 mediated immune surveillance have against viruses (Aim 3). Thus, the proposed study will attempt to delineate the molecular mechanisms underlying the host-viral interaction at a basic scientific level and will also provide the foundations for developing novel diagnostic and therapeutic strategies for emerging virus-associated disorders at the public health level.