PROTEOME-WIDE IDENTIFICATION OF RNA-BINDING PROTEINS PLAYING CRITICAL ROLES IN VIRUS INFECTION

Many viruses that infect humans have a genome made of RNA instead of DNA, including human immunodeficiency virus, hepatitis C virus and influenza virus. The viral enzymes involved in RNA replication display a high mutation rate, allowing rapid evolution of the virus, which helps it to evade immune defences and allows the emergence of resistance to antiviral drugs. RNA genomes are small, often encoding just a dozen proteins. By contrast, the human host cell dedicates ~1,500 RNA-binding proteins (RBPs) to RNA metabolism. Since viral genomes can only encode a handful of these proteins they rely on host proteins to complete their biological cycle. Host RBPs can also play another important role in infection, by acting as "sensors" that detect unusual molecular signatures present in viral RNAs and their replication intermediaries. Upon binding, these "sensors" trigger the antiviral response to alert neighbouring cells and provide an opportunity to block virus infection. Despite their relevance, the scope of RBPs involved in virus infection remains largely unknown. We propose, here, a new strategy to identify in a global manner the subset of RBPs implicated in infection using the prototypical Sindbis virus as a model. In brief, we will label viral RNA with a nucleotide analogue called 4-thiouridine (4SU). Upon irradiation, with 365 nm ultraviolet light, 4SU is activated acting as a "glue" that covalently links the viral RNA to the proteins interacting with it. These chemically "frozen" complexes will be captured using oligo(dT) beads as a "fishing net". The proteins "stuck" to the viral RNA will be identified by proteomic approaches. The levels or activity of key candidates will be altered using genetic tools or drugs to assess their consequences in the infection of Sindbis virus and other human RNA viruses. RBPs with a strong influence in infection will be studied in detail to understand their biological role. Our approach will identify targets for new antiviral strategies.