The catcher in the RIG-I.

Retinoic-acid inducible gene I (RIG-I) is a major pattern recognition receptor of the innate immune system. RIG-I is a cytoplasmic RNA helicase that is able to bind virus-specific RNA structures. Activated RIG-I switches into a conformation that locks the ligand RNA and signals via the MAVS-IRF-3 axis, resulting in the upregulation of antiviral interferons. Recent evidence suggests that the binding of RIG-I to regulatory RNA structures of two major human pathogens, influenza A virus and hepatitis B virus, can inhibit viral replication independent of the subsequent signal transduction. Thus, RIG-I rides a two-pronged attack, with an early-hitting, direct inhibition via occupancy of viral regulatory RNA structures, and a delayed response via signaling and induction of interferons.