title: A micrococcal nuclease homologue in RNAi effector complexes.
abstract: RNA interference (RNAi) regulates gene expression by the cleavage of messenger RNA, by mRNA degradation and by preventing protein synthesis. These effects are mediated by a ribonucleoprotein complex known as RISC (RNA-induced silencing complex). We have previously identified four Drosophila components (short interfering RNAs, Argonaute 2 (ref. 2), VIG and FXR) of a RISC enzyme that degrades specific mRNAs in response to a double-stranded-RNA trigger. Here we show that Tudor-SN (tudor staphylococcal nuclease)--a protein containing five staphylococcal/micrococcal nuclease domains and a tudor domain--is a component of the RISC enzyme in Caenorhabditis elegans, Drosophila and mammals. Although Tudor-SN contains non-canonical active-site sequences, we show that purified Tudor-SN exhibits nuclease activity similar to that of other staphylococcal nucleases. Notably, both purified Tudor-SN and RISC are inhibited by a specific competitive inhibitor of micrococcal nuclease. Tudor-SN is the first RISC subunit to be identified that contains a recognizable nuclease domain, and could therefore contribute to the RNA degradation observed in RNAi.
mesh_terms: D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000201:enzymology; D004331:Drosophila melanogaster / Q000201:enzymology; D046911:Macromolecular Substances; D008836:Micrococcal Nuclease / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D012323:RNA Processing, Post-Transcriptional; D034743:RNA-Induced Silencing Complex / Q000737:chemistry* / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D034743:RNA-Induced Silencing Complex; D008836:Micrococcal Nuclease