A multicomponent, ribonucleoprotein complex comprised of one of the family of argonaute proteins and the "guide strand" of the one of the 20- to 30-nucleotide small RNAs. RISC cleaves specific RNAs, which are targeted for degradation by homology to these small RNAs. Functions in regulating gene expression are determined by the specific argonaute protein and small RNA including siRNA (rna, small interfering), miRNA (MICRORNA), or piRNA (PIWI-INTERACTING RNA).