HRD4/NPL4 is required for the proteasomal processing of ubiquitinated ER proteins

Mol Biol Cell. 2001 Dec;12(12):4114-28. doi: 10.1091/mbc.12.12.4114.


We isolated a temperature-sensitive mutant, hrd4-1, deficient in ER-associated degradation (ERAD). The HRD4 gene was identical to NPL4, a gene previously implicated in nuclear transport. Using a diverse set of substrates and direct ubiquitination assays, our analysis revealed that HRD4/NPL4 is required for a poorly characterized step in ERAD after ubiquitination of target proteins but before their recognition by the 26S proteasome. Our data indicate that this lack of proteasomal processing of ubiquitinated proteins constitutes the primary defect in hrd4/npl4 mutant cells and explains the diverse set of hrd4/npl4 phenotypes. We also found that each member of the Cdc48p-Ufd1p-Npl4p complex is individually required for ERAD.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Active Transport, Cell Nucleus
  • Adenosine Triphosphatases
  • Cell Cycle Proteins / metabolism
  • Cysteine Endopeptidases / metabolism*
  • Endoplasmic Reticulum / chemistry*
  • Endoplasmic Reticulum / metabolism*
  • Fatty Acids, Unsaturated / metabolism
  • Flow Cytometry
  • Multienzyme Complexes / metabolism*
  • Mutation
  • Nuclear Pore Complex Proteins*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Nucleocytoplasmic Transport Proteins
  • Proteasome Endopeptidase Complex
  • Protein Processing, Post-Translational*
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Ubiquitin / metabolism*
  • Valosin Containing Protein
  • Vesicular Transport Proteins


  • Cell Cycle Proteins
  • Fatty Acids, Unsaturated
  • Multienzyme Complexes
  • NPL4 protein, S cerevisiae
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • Nucleocytoplasmic Transport Proteins
  • Saccharomyces cerevisiae Proteins
  • UFD1 protein, S cerevisiae
  • Ubiquitin
  • Vesicular Transport Proteins
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Adenosine Triphosphatases
  • CDC48 protein, S cerevisiae
  • Valosin Containing Protein