A protein sensor for siRNA asymmetry.
To act as guides in the RNA interference (RNAi) pathway, small interfering RNAs (siRNAs) must be unwound into their component strands, then assembled with proteins to form the RNA-induced silencing complex (RISC), which catalyzes target messenger RNA cleavage. Thermodynamic differences in the base-pairing stabilities of the 5' ends of the two approximately 21-nucleotide siRNA strands determine which siRNA strand is assembled into the RISC. We show that in Drosophila, the orientation of the Dicer-2/R2D2 protein heterodimer on the siRNA duplex determines which siRNA strand associates with the core RISC protein Argonaute 2. R2D2 binds the siRNA end with the greatest double-stranded character, thereby orienting the heterodimer on the siRNA duplex. Strong R2D2 binding requires a 5'-phosphate on the siRNA strand that is excluded from the RISC. Thus, R2D2 is both a protein sensor for siRNA thermodynamic asymmetry and a licensing factor for entry of authentic siRNAs into the RNAi pathway.
Tomari
Yukihide
Y
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Matranga
Christian
C
Haley
Benjamin
B
Martinez
Natalia
N
Zamore
Phillip D
PD
D000818:Animals; D060565:Argonaute Proteins; D019281:Dimerization; D004330:Drosophila / Q000196:embryology / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism*; D008027:Light; D008156:Luciferases / Q000235:genetics; D009690:Nucleic Acid Conformation; D020365:RNA Helicases / Q000378:metabolism*; D034622:RNA Interference; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000378:metabolism; D034741:RNA, Small Interfering / Q000737:chemistry* / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D034743:RNA-Induced Silencing Complex / Q000378:metabolism*; D043244:Ribonuclease III; D013482:Superoxide Dismutase / Q000235:genetics; D013816:Thermodynamics; D014498:Uracil / Q000031:analogs & derivatives* / Q000032:analysis
C433807:AGO2 protein, Drosophila; D060565:Argonaute Proteins; D029721:Drosophila Proteins; C478068:R2D2 protein, Drosophila; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D034743:RNA-Induced Silencing Complex; D014498:Uracil; D008156:Luciferases; D013482:Superoxide Dismutase; C478069:DCR-2 protein, Drosophila; D043244:Ribonuclease III; D020365:RNA Helicases; C048747:5-iodouracil