title: Immature small ribosomal subunits can engage in translation initiation in Saccharomyces cerevisiae.
abstract: It is generally assumed that, in Saccharomyces cerevisiae, immature 40S ribosomal subunits are not competent for translation initiation. Here, we show by different approaches that, in wild-type conditions, a portion of pre-40S particles (pre-SSU) associate with translating ribosomal complexes. When cytoplasmic 20S pre-rRNA processing is impaired, as in Rio1p- or Nob1p-depleted cells, a large part of pre-SSUs is associated with translating ribosomes complexes. Loading of pre-40S particles onto mRNAs presumably uses the canonical pathway as translation-initiation factors interact with 20S pre-rRNA. However, translation initiation is not required for 40S ribosomal subunit maturation. We also provide evidence suggesting that cytoplasmic 20S pre-rRNAs that associate with translating complexes are turned over by the no go decay (NGD) pathway, a process known to degrade mRNAs on which ribosomes are stalled. We propose that the cytoplasmic fate of 20S pre-rRNA is determined by the balance between pre-SSU processing kinetics and sensing of ribosome-like particles loaded onto mRNAs by the NGD machinery, which acts as an ultimate ribosome quality check point.
authors.affiliation: Laboratoire de Biologie Moléculaire Eucaryote, Université de Toulouse, Université Paul Sabatier, Toulouse, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Soudet
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Gélugne
authors.forename: Kamila
authors.initials: K
authors.lastname: Belhabich-Baumas
authors.forename: Michèle
authors.initials: M
authors.lastname: Caizergues-Ferrer
authors.forename: Annie
authors.initials: A
authors.lastname: Mougin
mesh_terms: D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics; D015977:Eukaryotic Initiation Factor-1 / Q000235:genetics / Q000378:metabolism; D039621:Eukaryotic Initiation Factor-3 / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010442:Peptide Chain Initiation, Translational; D011132:Polyribosomes / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D054683:Ribosome Subunits, Large, Eukaryotic / Q000235:genetics / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000235:genetics* / Q000378:metabolism*; D012270:Ribosomes / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D004271:DNA, Fungal; D015977:Eukaryotic Initiation Factor-1; D039621:Eukaryotic Initiation Factor-3; C405962:NOB1 protein, S cerevisiae; D009687:Nuclear Proteins; C050998:Prt1 protein, S cerevisiae; D012322:RNA Precursors; D012331:RNA, Fungal; C111889:RPG1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C026022:eukaryotic peptide initiation factor-1A; D017346:Protein Serine-Threonine Kinases; C462948:Rio1 protein, S cerevisiae