Nature Cell Biology
3, 24 - 29 (2001)
Published online: 4 December 2000; | doi:10.1038/35050524
Hrd1p/Der3p is a membrane-anchored ubiquitin ligase required for ER-associated degradationNathan W. Bays1, Richard G. Gardner1, Linda P. Seelig1, Claudio A. Joazeiro2
& Randolph Y. Hampton11
Section of Cell and Developmental Biology, Division of Biology, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0347, USA
2
Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037-1099, USA
Correspondence should be addressed to Randolph Y. Hampton e-mail:rhampton@ucsd.eduIn eukaryotes, endoplasmic reticulum-associated degradation (ERAD) functions in cellular quality control and regulation of normal ER-resident proteins. ERAD proceeds by the ubiquitin−proteasome pathway, in which the covalent attachment of ubiquitin to proteins targets them for proteasomal degradation. Ubiquitin−protein ligases (E3s) play a crucial role in this process by recognizing target proteins and initiating their ubiquitination. Here we show that Hrd1p, which is identical to Der3p, is an E3 for ERAD. Hrd1p is required for the degradation and ubiquitination of several ERAD substrates and physically associates with relevant ubiquitin-conjugating enzymes (E2s). A soluble Hrd1 fusion protein shows E3 activity in vitro — catalysing the ubiquitination of itself and test proteins. In this capacity, Hrd1p has an apparent preference for misfolded proteins. We also show that Hrd1p functions as an E3 in vivo, using only Ubc7p or Ubc1p to specifically program the ubiquitination of ERAD substrates.
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