Argonaute (AGO) proteins play an important role in small-RNA-mediated (miRNA, siRNA and piRNA) gene-silencing events and form the core constituent of the RNA-induced silencing complex (RISC). The PIWI domain of AGO proteins resembles RNase-H and accounts for their endonuclease activity that cleaves target mRNA complementary to the bound small RNA. (Adapted from PMID: 29447113).