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Ubr1 and Ubr2 function in a quality control pathway for degradation of unfolded cytosolic proteins.

Quality control systems facilitate polypeptide folding and degradation to maintain protein homeostasis. Molecular chaperones promote folding, whereas the ubiquitin/proteasome system mediates degradation. We show here that Saccharomyces cerevisiae Ubr1 and Ubr2 ubiquitin ligases promote degradation of unfolded or misfolded cytosolic polypeptides. Ubr1 also catalyzes ubiquitinylation of denatured but not native luciferase in a purified system. This activity is based on the direct interaction of denatured luciferase with Ubr1, although Hsp70 stimulates polyubiquitinylation of the denatured substrate. We also report that loss of Ubr1 and Ubr2 function suppressed the growth arrest phenotype resulting from chaperone mutation. This correlates with increased protein kinase maturation and indicates partitioning of foldable conformers toward the proteasome. Our findings, based on the efficiency of this quality control system, suggest that the cell trades growth potential to avert the potential toxicity associated with accumulation of unfolded or misfolded proteins. Ubr1 and Ubr2 therefore represent E3 components of a novel quality control pathway for proteins synthesized on cytosolic ribosomes.

Pubmed ID: 20462952


  • Nillegoda NB
  • Theodoraki MA
  • Mandal AK
  • Mayo KJ
  • Ren HY
  • Sultana R
  • Wu K
  • Johnson J
  • Cyr DM
  • Caplan AJ


Molecular biology of the cell

Publication Data

July 1, 2010

Associated Grants

  • Agency: NCRR NIH HHS, Id: 5G12-RR03060
  • Agency: NIGMS NIH HHS, Id: R01 GM067785
  • Agency: NIGMS NIH HHS, Id: R01GM067785
  • Agency: NIGMS NIH HHS, Id: R01GM70596
  • Agency: NCI NIH HHS, Id: U54CA132378

Mesh Terms

  • Animals
  • Cyclic AMP-Dependent Protein Kinases
  • HSP70 Heat-Shock Proteins
  • Luciferases, Firefly
  • Peptides
  • Proteasome Endopeptidase Complex
  • Proteasome Inhibitors
  • Protein Conformation
  • Protein Denaturation
  • Protein Folding
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin-Protein Ligases
  • Ubiquitination
  • Unfolded Protein Response