title: The 3'-to-5' exoribonuclease Nibbler shapes the 3' ends of microRNAs bound to Drosophila Argonaute1.
abstract: BACKGROUND
  MicroRNAs (miRNAs) are ~22 nucleotide (nt) small RNAs that control development, physiology, and pathology in animals and plants. Production of miRNAs involves the sequential processing of primary hairpin-containing RNA polymerase II transcripts by the RNase III enzymes Drosha in the nucleus and Dicer in the cytoplasm. miRNA duplexes then assemble into Argonaute proteins to form the RNA-induced silencing complex (RISC). In mature RISC, a single-stranded miRNA directs the Argonaute protein to bind partially complementary sequences, typically in the 3' untranslated regions of messenger RNAs, repressing their expression.
  
  
  RESULTS
  Here, we show that after loading into Argonaute1 (Ago1), more than a quarter of all Drosophila miRNAs undergo 3' end trimming by the 3'-to-5' exoribonuclease Nibbler (CG9247). Depletion of Nibbler by RNA interference (RNAi) reveals that miRNAs are frequently produced by Dicer-1 as intermediates that are longer than ~22 nt. Trimming of miRNA 3' ends occurs after removal of the miRNA* strand from pre-RISC and may be the final step in RISC assembly, ultimately enhancing target messenger RNA repression. In vivo, depletion of Nibbler by RNAi causes developmental defects.
  
  
  CONCLUSIONS
  We provide a molecular explanation for the previously reported heterogeneity of miRNA 3' ends and propose a model in which Nibbler converts miRNAs into isoforms that are compatible with the preferred length of Ago1-bound small RNAs.
authors: Howard Hughes Medical Institute and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors: Bo W
authors: BW
authors: Han
authors: Jui-Hung
authors: JH
authors: Hung
authors: Zhiping
authors: Z
authors: Weng
authors: Phillip D
authors: PD
authors: Zamore
authors: Stefan L
authors: SL
authors: Ameres
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D005095:Exoribonucleases / Q000378:metabolism*; D035683:MicroRNAs / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D020365:RNA Helicases / Q000378:metabolism; D034622:RNA Interference; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000378:metabolism; D043244:Ribonuclease III / Q000378:metabolism
chemical_list: C489654:AGO1 protein, Drosophila; D060565:Argonaute Proteins; D029721:Drosophila Proteins; C570893:MIRN34 microRNA, Drosophila; D035683:MicroRNAs; D012333:RNA, Messenger; D034743:RNA-Induced Silencing Complex; C515033:Dcr-1 protein, Drosophila; D005095:Exoribonucleases; C570892:Nbr protein, Drosophila; D043244:Ribonuclease III; C493335:drosha protein, Drosophila; D020365:RNA Helicases