title: Molecular composition of IMP1 ribonucleoprotein granules.
abstract: Localized mRNAs are transported to sites of local protein synthesis in large ribonucleoprotein (RNP) granules, but their molecular composition is incompletely understood. Insulin-like growth factor II mRNA-binding protein (IMP) zip code-binding proteins participate in mRNA localization, and in motile cells IMP-containing granules are dispersed around the nucleus and in cellular protrusions. We isolated the IMP1-containing RNP granules and found that they represent a unique RNP entity distinct from neuronal hStaufen and/or fragile X mental retardation protein granules, processing bodies, and stress granules. Granules were 100-300 nm in diameter and consisted of IMPs, 40 S ribosomal subunits, shuttling heterologous nuclear RNPs, poly(A)-binding proteins, and mRNAs. Moreover granules contained CBP80 and factors belonging to the exon junction complex and lacked eIF4E, eIF4G, and 60 S ribosomal subunits, indicating that embodied mRNAs are not translated. Granules embodied mRNAs corresponding to about 3% of the human embryonic kidney 293 mRNA transcriptome. Messenger RNAs encoding proteins participating in the secretory pathway and endoplasmic reticulum-associated quality control, as well as ubiquitin-dependent metabolism, were enriched in the granules, reinforcing the concept of RNP granules as post-transcriptional operons.
authors.affiliation: Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Jønson
authors.forename: Jonas
authors.initials: J
authors.lastname: Vikesaa
authors.forename: Anders
authors.initials: A
authors.lastname: Krogh
authors.forename: Lars K
authors.initials: LK
authors.lastname: Nielsen
authors.forename: Thomas vO
authors.initials: Tv
authors.lastname: Hansen
authors.forename: Rehannah
authors.initials: R
authors.lastname: Borup
authors.forename: Anders H
authors.initials: AH
authors.lastname: Johnsen
authors.forename: Jan
authors.initials: J
authors.lastname: Christiansen
authors.forename: Finn C
authors.initials: FC
authors.lastname: Nielsen
mesh_terms: D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000378:metabolism; D006801:Humans; D053858:Metabolic Networks and Pathways; D018625:Microscopy, Atomic Force; D040901:Proteomics; D012333:RNA, Messenger / Q000032:analysis; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D012261:Ribonucleoproteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D003598:Cytoskeletal Proteins; D051860:Fragile X Messenger Ribonucleoprotein 1; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C497683:FMR1 protein, human; C406144:IGF2BP1 protein, human; C492185:STAU1 protein, human