title: MicroRNAs block assembly of eIF4F translation initiation complex in Drosophila.
abstract: miRNAs silence their complementary target mRNAs by translational repression as well as by poly(A) shortening and mRNA decay. In Drosophila, miRNAs are typically incorporated into Argonaute1 (Ago1) to form the effector complex called RNA-induced silencing complex (RISC). Ago1-RISC associates with a scaffold protein GW182, which recruits additional silencing factors. We have previously shown that miRNAs repress translation initiation by blocking formation of the 48S and 80S ribosomal complexes. However, it remains unclear how ribosome recruitment is impeded. Here, we examined the assembly of translation initiation factors on the target mRNA under repression. We show that Ago1-RISC induces dissociation of eIF4A, a DEAD-box RNA helicase, from the target mRNA without affecting 5' cap recognition by eIF4E in a manner independent of GW182. In contrast, direct tethering of GW182 promotes dissociation of both eIF4E and eIF4A. We propose that miRNAs act to block the assembly of the eIF4F complex during translation initiation.
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Medical Genome Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Fukaya
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Hiro-Oki
authors.initials: HO
authors.lastname: Iwakawa
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Medical Genome Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan. Electronic address: tomari@iam.u-tokyo.ac.jp.
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Tomari
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology; D039601:Eukaryotic Initiation Factor-4A / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism*; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008957:Models, Genetic; D010442:Peptide Chain Initiation, Translational; D012333:RNA, Messenger / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000378:metabolism
chemical_list: C489654:AGO1 protein, Drosophila; D060565:Argonaute Proteins; D029721:Drosophila Proteins; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; C513405:Gw protein, Drosophila; D035683:MicroRNAs; D012333:RNA, Messenger; D034743:RNA-Induced Silencing Complex; D039601:Eukaryotic Initiation Factor-4A