title: A ribonuclease coordinates siRNA amplification and mRNA cleavage during RNAi.
abstract: Effective silencing by RNA-interference (RNAi) depends on mechanisms that amplify and propagate the silencing signal. In some organisms, small-interfering RNAs (siRNAs) are amplified from target mRNAs by RNA-dependent RNA polymerase (RdRP). Both RdRP recruitment and mRNA silencing require Argonaute proteins, which are generally thought to degrade RNAi targets by directly cleaving them. However, in C. elegans, the enzymatic activity of the primary Argonaute, RDE-1, is not required for silencing activity. We show that RDE-1 can instead recruit an endoribonuclease, RDE-8, to target RNA. RDE-8 can cleave RNA in vitro and is needed for the production of 3' uridylated fragments of target mRNA in vivo. We also find that RDE-8 promotes RdRP activity, thereby ensuring amplification of siRNAs. Together, our findings suggest a model in which RDE-8 cleaves target mRNAs to mediate silencing, while generating 3' uridylated mRNA fragments to serve as templates for the RdRP-directed amplification of the silencing signal.
authors: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA; Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei 115, Taiwan.
authors: Hsin-Yue
authors: HY
authors: Tsai
authors: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors: Chun-Chieh G
authors: CC
authors: Chen
authors: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors: Darryl
authors: D
authors: Conte
authors: Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors: James J
authors: JJ
authors: Moresco
authors: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA; Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028 Lisboa, Portugal.
authors: Daniel A
authors: DA
authors: Chaves
authors: CREST, Japan Science and Technology Agency and Department of Physiology, Tokyo Women's Medical University School of Medicine, Tokyo 162-8666, Japan.
authors: Shohei
authors: S
authors: Mitani
authors: Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors: John R
authors: JR
authors: Yates
authors: Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei 115, Taiwan.
authors: Ming-Daw
authors: MD
authors: Tsai
authors: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA; Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA. Electronic address: craig.mello@umassmed.edu.
authors: Craig C
authors: CC
authors: Mello
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism; D004722:Endoribonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D034622:RNA Interference; D012330:RNA, Double-Stranded; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism; D043244:Ribonuclease III / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029742:Caenorhabditis elegans Proteins; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C122185:rde-1 protein, C elegans; D012324:RNA-Dependent RNA Polymerase; D004722:Endoribonucleases; C000597191:RDE-8 protein, C elegans; D043244:Ribonuclease III
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