AGO2 is a crucial component of the RNA-induced silencing complex (RISC) which when bound to an RNA molecule inhibits gene expression . The structure of AGO2 complex (4W5O) contains a protein of 859 residues (residues 1-21 not modeled), a guide RNA of 21 nucleotides and a target RNA of 11 nucleotides. The guide RNA binds to Ago2 mainly from the 5' end which contains the seed sequence (nucleotides 2-7) which are crucial to the binding to the complementary mRNA strand . The 3' end of the guide RNA is bound to the most flexible part of Ago2, the PAZ domain (residues 235-348) . The target RNA is mainly forming interactions with the guide RNA strand, with a few flanking nucleotides interacting with the Ago2 surface.