Immature small ribosomal subunits can engage in translation initiation in Saccharomyces cerevisiae.
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.
Soudet
Julien
J
Laboratoire de Biologie Moléculaire Eucaryote, Université de Toulouse, Université Paul Sabatier, Toulouse, France.
Gélugne
Jean-Paul
JP
Belhabich-Baumas
Kamila
K
Caizergues-Ferrer
Michèle
M
Mougin
Annie
A
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
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