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Cdc48-associated complex bound to 60S particles is required for the clearance of aberrant translation products

Quentin Defenouillère1, Yanhua Yao, John Mouaikel

  • 1Institut Pasteur, Génétique des Interactions Macromoléculaires, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 3525, F-75724 Paris, France.

Proceedings of the National Academy of Sciences of the United States of America
|March 13, 2013
PubMed

Insights

Researchers identified Tae2 and Rqc1, crucial for degrading non-stop proteins. These factors, along with Ltn1 and Cdc48, associate with 60S ribosomal subunits to target aberrant polypeptides for proteasomal degradation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Protein Degradation

Background:

  • Ribosome stalling on eukaryotic messenger RNAs (mRNAs) initiates cotranslational RNA and protein degradation via conserved pathways.
  • mRNAs lacking stop codons are degraded by the exosome-SKI complex, while aberrant nascent polypeptides are ubiquitinated by E3 ligases (Ltn1, Not4) and targeted to the proteasome.

Purpose of the Study:

  • To elucidate the molecular mechanisms linking translation arrest to polypeptide degradation.
  • To identify novel factors involved in the degradation of polypeptides synthesized from non-stop mRNAs.

Main Methods:

  • Genetic screens using SKI and LTN1 mutants.
  • Co-immunoprecipitation assays to identify associated factors.
  • Polysome gradient analyses to study pathway intermediates.

Main Results:

  • Identified translation-associated element 2 (Tae2) and ribosome quality control 1 (Rqc1) as novel factors associated with 60S ribosomal subunits.
  • Tae2, Rqc1, and the AAA-ATPase Cdc48 are essential for non-stop protein decay (NSPD).
  • Ltn1 and Rqc1 are critical for recruiting Cdc48 to 60S particles, facilitating progressive polyubiquitination of non-stop peptides.

Conclusions:

  • A novel pathway involving Tae2, Rqc1, Ltn1, and Cdc48 mediates the degradation of polypeptides from non-stop mRNAs.
  • Ubiquitination initiates on the 80S ribosome and continues on the 60S subunit, where Cdc48 escorts the substrate for proteasomal degradation.

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