Argonaute2, a link between genetic and biochemical analyses of RNAi

Double-stranded RNA induces potent and specific gene silencing through a pr ocess referred to as RNA interference (RNAi) or posttranscriptional gene si lencing (PTGS). RNAi is mediated by RNA-induced silencing complex (RISC), a sequence-specific, multicomponent nuclease that destroys messenger RNAs ho mologous to the silencing trigger. RISC is known to contain short RNAs (sim ilar to 22 nucleotides) derived from the double-stranded RNA trigger, but t he protein components of this activity are unknown. Here, we report the bio chemical purification of the RNAi effector nuclease from cultured Drosophil a cells. The active fraction contains a ribonucleoprotein complex of simila r to 500 kilodaltons. Protein microsequencing reveals that one constituent of this complex is a member of the Argonaute family of proteins, which are essential for gene silencing in Caenorhabditis elegans, Neurospora, and Ara bidopsis. This observation begins the process of forging links between gene tic analysis of RNAi from diverse organisms and the biochemical model of RN Ai that is emerging from Drosophila in vitro systems.