title: The nuclear poly(A) polymerase and Exosome cofactor Trf5 is recruited cotranscriptionally to nucleolar surveillance.
abstract: Terminal balls detected at the 5'-end of nascent ribosomal transcripts act as pre-rRNA processing complexes and are detected in all eukaryotes examined, resulting in illustrious Christmas tree images. Terminal balls (also known as SSU-processomes) compaction reflects the various stages of cotranscriptional ribosome assembly. Here, we have followed SSU-processome compaction in vivo by use of a chromatin immunoprecipitation (Ch-IP) approach and shown, in agreement with electron microscopy analysis of Christmas trees, that it progressively condenses to come in close proximity to the 5'-end of the 25S rRNA gene. The SSU-processome is comprised of independent autonomous building blocks that are loaded onto nascent pre-rRNAs and assemble into catalytically active pre-rRNA processing complexes in a stepwise and highly hierarchical process. Failure to assemble SSU-processome subcomplexes with proper kinetics triggers a nucleolar surveillance pathway that targets misassembled pre-rRNAs otherwise destined to mature into small subunit 18S rRNA for polyadenylation, preferentially by TRAMP5, and degradation by the 3' to 5' exoribonucleolytic activity of the Exosome. Trf5 colocalized with nascent pre-rRNPs, indicating that this nucleolar surveillance initiates cotranscriptionally.
authors.affiliation: Fonds de la Recherche Scientifique (FRS-FNRS), AcadémieWallonie-Bruxelles, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, Charleroi-Gosselies, B-6041 Belgium.
authors.forename: Maxime
authors.initials: M
authors.lastname: Wery
authors.forename: Sabine
authors.initials: S
authors.lastname: Ruidant
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Schillewaert
authors.forename: Nathalie
authors.initials: N
authors.lastname: Leporé
authors.forename: Denis L J
authors.initials: DL
authors.lastname: Lafontaine
mesh_terms: D002466:Cell Nucleolus / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D012322:RNA Precursors / Q000235:genetics* / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D012322:RNA Precursors; D029701:Saccharomyces cerevisiae Proteins; D012321:DNA-Directed RNA Polymerases; C506067:Trf5 protein, S cerevisiae