title: L-Ilf3 and L-NF90 traffic to the nucleolus granular component: alternatively-spliced exon 3 encodes a nucleolar localization motif.
abstract: Ilf3 and NF90, two proteins containing double-stranded RNA-binding domains, are generated by alternative splicing and involved in several functions. Their heterogeneity results from posttranscriptional and posttranslational modifications. Alternative splicing of exon 3, coding for a 13 aa N-terminal motif, generates for each protein a long and short isoforms. Subcellular fractionation and localization of recombinant proteins showed that this motif acts as a nucleolar localization signal. Deletion and substitution mutants identified four arginines, essential for nucleolar targeting, and three histidines to stabilize the proteins within the nucleolus. The short isoforms are never found in the nucleoli, whereas the long isoforms are present in the nucleoplasm and the nucleoli. For Ilf3, only the posttranslationally-unmodified long isoform is nucleolar, suggesting that this nucleolar targeting is abrogated by posttranslational modifications. Confocal microscopy and FRAP experiments have shown that the long Ilf3 isoform localizes to the granular component of the nucleolus, and that L-Ilf3 and L-NF90 exchange rapidly between nucleoli. The presence of this 13 aminoacid motif, combined with posttranslational modifications, is responsible for the differences in Ilf3 and NF90 isoforms subcellular localizations. The protein polymorphism of Ilf3/NF90 and the various subcellular localizations of their isoforms may partially explain the various functions previously reported for these proteins.
authors.affiliation: UPMC Univ Paris 06, UMR 7622, Laboratoire de Biologie du Développement, Paris, France.
authors.forename: Wildriss
authors.initials: W
authors.lastname: Viranaicken
authors.forename: Laila
authors.initials: L
authors.lastname: Gasmi
authors.forename: Alexandre
authors.initials: A
authors.lastname: Chaumet
authors.forename: Christiane
authors.initials: C
authors.lastname: Durieux
authors.forename: Virginie
authors.initials: V
authors.lastname: Georget
authors.forename: Philippe
authors.initials: P
authors.lastname: Denoulet
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Larcher
mesh_terms: D017398:Alternative Splicing / Q000187:drug effects / Q000235:genetics*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism*; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D005091:Exons / Q000235:genetics*; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D050779:Nuclear Factor 90 Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D059368:RNA Isoforms / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: C429643:ILF3 protein, human; D050779:Nuclear Factor 90 Proteins; D020033:Protein Isoforms; D021382:Protein Sorting Signals; D059368:RNA Isoforms; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004004:Dichlororibofuranosylbenzimidazole