title: Hsc70/Hsp90 chaperone machinery mediates ATP-dependent RISC loading of small RNA duplexes.
abstract: Small silencing RNAs--small interfering RNAs (siRNAs) or microRNAs (miRNAs)--direct posttranscriptional gene silencing of their mRNA targets as guides for the RNA-induced silencing complex (RISC). Both siRNAs and miRNAs are born double stranded. Surprisingly, loading these small RNA duplexes into Argonaute proteins, the core components of RISC, requires ATP, whereas separating the two small RNA strands within Argonaute does not. Here we show that the Hsc70/Hsp90 chaperone machinery is required to load small RNA duplexes into Argonaute proteins, but not for subsequent strand separation or target cleavage. We envision that the chaperone machinery uses ATP and mediates a conformational opening of Ago proteins so that they can receive bulky small RNA duplexes. Our data suggest that the chaperone machinery may serve as the driving force for the RISC assembly pathway.
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Iwasaki
authors.forename: Maki
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Mayuko
authors.initials: M
authors.lastname: Yoda
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Sakaguchi
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Tomari
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D034743:RNA-Induced Silencing Complex / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D050883:HSC70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D035683:MicroRNAs; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D034743:RNA-Induced Silencing Complex; D000255:Adenosine Triphosphate