title: Sorting of Drosophila small silencing RNAs partitions microRNA* strands into the RNA interference pathway.
abstract: In flies, small silencing RNAs are sorted between Argonaute1 (Ago1), the central protein component of the microRNA (miRNA) pathway, and Argonaute2 (Ago2), which mediates RNA interference. Extensive double-stranded character-as is found in small interfering RNAs (siRNAs)-directs duplexes into Ago2, whereas central mismatches, like those found in miRNA/miRNA* duplexes, direct duplexes into Ago1. Central to this sorting decision is the affinity of the small RNA duplex for the Dcr-2/R2D2 heterodimer, which loads small RNAs into Ago2. Here, we show that while most Drosophila miRNAs are bound to Ago1, miRNA* strands accumulate bound to Ago2. Like siRNA loading, efficient loading of miRNA* strands in Ago2 favors duplexes with a paired central region and requires both Dcr-2 and R2D2. Those miRNA and miRNA* sequences bound to Ago2, like siRNAs diced in vivo from long double-stranded RNA, typically begin with cytidine, whereas Ago1-bound miRNA and miRNA* disproportionately begin with uridine. Consequently, some pre-miRNA generate two or more isoforms from the same side of the stem that differentially partition between Ago1 and Ago2. Our findings provide the first genome-wide test for the idea that Drosophila small RNAs are sorted between Ago1 and Ago2 according to their duplex structure and the identity of their first nucleotide.
authors.affiliation: Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School,Worcester, Massachusetts 01605, USA.
authors.forename: Megha
authors.initials: M
authors.lastname: Ghildiyal
authors.forename: Jia
authors.initials: J
authors.lastname: Xu
authors.forename: Hervé
authors.initials: H
authors.lastname: Seitz
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Weng
authors.forename: Phillip D
authors.initials: PD
authors.lastname: Zamore
mesh_terms: D000818:Animals; D060565:Argonaute Proteins; D001483:Base Sequence / Q000502:physiology; D001665:Binding Sites / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins / Q000378:metabolism; D004625:Embryo, Nonmammalian; D039642:Eukaryotic Initiation Factors / Q000378:metabolism; D035683:MicroRNAs / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D034622:RNA Interference / Q000502:physiology*; D034443:RNA Transport / Q000235:genetics / Q000502:physiology; D034741:RNA, Small Interfering / Q000737:chemistry / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics
chemical_list: C489654:AGO1 protein, Drosophila; C433807:AGO2 protein, Drosophila; D060565:Argonaute Proteins; D029721:Drosophila Proteins; D039642:Eukaryotic Initiation Factors; D035683:MicroRNAs; D034741:RNA, Small Interfering; D034743:RNA-Induced Silencing Complex