Required for RNA-mediated gene silencing (RNAi) by the RNA-induced silencing complex (RISC). The 'minimal RISC' appears to include ago2 bound to a short guide RNA such as a microRNA (miRNA) or short interfering RNA (siRNA). These guide RNAs direct RISC to complementary mRNAs that are targets for RISC-mediated gene silencing. The precise mechanism of gene silencing depends on the degree of complementarity between the miRNA or siRNA and its target. Binding of RISC to a perfectly complementary mRNA generally results in silencing due to endonucleolytic cleavage of the mRNA specifically by ago2. Binding of RISC to a partially complementary mRNA results in silencing through inhibition of translation, and this is independent of endonuclease activity. The inhibition of translational initiation leads to the accumulation of the affected mRNA in cytoplasmic processing bodies (P-bodies), where mRNA degradation may subsequently occur. endonucleolytic cleavage to 5'-phosphomonoester. Component of the RISC loading complex (RLC), or micro-RNA (miRNA) loading complex (miRLC), which is composed of dicer1, ago2 and tarbp2. Note that the trimeric RLC/miRLC is also referred to as RISC. The Piwi domain may perform RNA cleavage by a mechanism similar to that of RNase H. However, while RNase H utilizes a triad of Asp-Asp-Glu (DDE) for metal ion coordination, this protein appears to utilize a triad of Asp-Asp-His (DDH). Belongs to the argonaute family. Ago subfamily.