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An HRD/DER-independent ER quality control mechanism involves Rsp5p-dependent ubiquitination and ER-Golgi transport.

We have identified a new pathway of ER-associated degradation in Saccharomyces cerevisiae that functions separately from the HRD/DER pathway comprised of Hrd1p, Hrd3p, Der1p, and Ubc7p. This pathway, termed Hrd1p independent-proteolysis (HIP), is capable of recognizing and degrading both lumenal (CPY* and PrA*), and integral membrane proteins (Sec61-2p) that misfold in the ER. CPY* overexpression likely saturates the HRD/DER pathway and activates the HIP pathway, so the slowed degradation kinetics of CPY* in a hrd1 Delta strain is restored to a wild-type rate when CPY* is overexpressed. Substrates of HIP require vesicular trafficking between the ER and Golgi apparatus before degradation by the ubiquitin-proteasome system. Ubiquitination of HIP substrates does not involve the HRD/DER pathway ubiquitin ligase Hrd1p, but instead uses another ubiquitin ligase, Rsp5p. HIP is regulated by the unfolded protein response as Ire1p is necessary for the degradation of CPY* when overexpressed, but not when CPY* is expressed at normal levels. Both the HIP and HRD/DER pathways contribute to the degradation of CPY*, and only by eliminating both is CPY* degradation completely blocked.

Pubmed ID: 12105183


  • Haynes CM
  • Caldwell S
  • Cooper AA


The Journal of cell biology

Publication Data

July 8, 2002

Associated Grants

  • Agency: NIGMS NIH HHS, Id: GM55848

Mesh Terms

  • Cytosol
  • Dose-Response Relationship, Drug
  • Endoplasmic Reticulum
  • Endosomal Sorting Complexes Required for Transport
  • Fungal Proteins
  • Golgi Apparatus
  • Kinetics
  • Ligases
  • Membrane Glycoproteins
  • Membrane Proteins
  • Models, Biological
  • Precipitin Tests
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Time Factors
  • Ubiquitin
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitin-Protein Ligase Complexes
  • Ubiquitin-Protein Ligases