title: Protein quality control at the inner nuclear membrane.
abstract: The nuclear envelope is a double membrane that separates the nucleus from the cytoplasm. The inner nuclear membrane (INM) functions in essential nuclear processes including chromatin organization and regulation of gene expression. The outer nuclear membrane is continuous with the endoplasmic reticulum and is the site of membrane protein synthesis. Protein homeostasis in this compartment is ensured by endoplasmic-reticulum-associated protein degradation (ERAD) pathways that in yeast involve the integral membrane E3 ubiquitin ligases Hrd1 and Doa10 operating with the E2 ubiquitin-conjugating enzymes Ubc6 and Ubc7 (refs 2, 3). However, little is known about protein quality control at the INM. Here we describe a protein degradation pathway at the INM in yeast (Saccharomyces cerevisiae) mediated by the Asi complex consisting of the RING domain proteins Asi1 and Asi3 (ref. 4). We report that the Asi complex functions together with the ubiquitin-conjugating enzymes Ubc6 and Ubc7 to degrade soluble and integral membrane proteins. Genetic evidence suggests that the Asi ubiquitin ligase defines a pathway distinct from, but complementary to, ERAD. Using unbiased screening with a novel genome-wide yeast library based on a tandem fluorescent protein timer, we identify more than 50 substrates of the Asi, Hrd1 and Doa10 E3 ubiquitin ligases. We show that the Asi ubiquitin ligase is involved in degradation of mislocalized integral membrane proteins, thus acting to maintain and safeguard the identity of the INM.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Khmelinskii
authors.affiliation: 1] Centre National de la Recherche Scientifique, UMR 6290, 35000 Rennes, France [2] Institut de Génétique et Développement de Rennes, Université de Rennes 1, 35000 Rennes, France.
authors.forename: Ewa
authors.initials: E
authors.lastname: Blaszczak
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20B, SE-106 91 Stockholm, Sweden.
authors.forename: Marina
authors.initials: M
authors.lastname: Pantazopoulou
authors.affiliation: 1] Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstraße 1, 69117 Heidelberg, Germany [2] Computational Genome Biology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 580, 69120 Heidelberg, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Fischer
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20B, SE-106 91 Stockholm, Sweden.
authors.forename: Deike J
authors.initials: DJ
authors.lastname: Omnus
authors.affiliation: 1] Centre National de la Recherche Scientifique, UMR 6290, 35000 Rennes, France [2] Institut de Génétique et Développement de Rennes, Université de Rennes 1, 35000 Rennes, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Le Dez
authors.affiliation: 1] Centre National de la Recherche Scientifique, UMR 6290, 35000 Rennes, France [2] Institut de Génétique et Développement de Rennes, Université de Rennes 1, 35000 Rennes, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Brossard
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20B, SE-106 91 Stockholm, Sweden.
authors.forename: Alexander
authors.initials: A
authors.lastname: Gunnarsson
authors.affiliation: Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstraße 1, 69117 Heidelberg, Germany.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Barry
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Meurer
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kirrmaier
authors.affiliation: Department of Molecular Genetics, Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, 160 College St, Toronto, Ontario M5S 3E1, Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: Boone
authors.affiliation: Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstraße 1, 69117 Heidelberg, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Huber
authors.affiliation: 1] Centre National de la Recherche Scientifique, UMR 6290, 35000 Rennes, France [2] Institut de Génétique et Développement de Rennes, Université de Rennes 1, 35000 Rennes, France.
authors.forename: Gwenaël
authors.initials: G
authors.lastname: Rabut
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20B, SE-106 91 Stockholm, Sweden.
authors.forename: Per O
authors.initials: PO
authors.lastname: Ljungdahl
authors.affiliation: 1] Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany [2] Cell Morphogenesis and Signal Transduction, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Knop
mesh_terms: D060746:Endoplasmic Reticulum-Associated Degradation / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D009685:Nuclear Envelope / Q000201:enzymology* / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism
chemical_list: C438144:ASI1 protein, S cerevisiae; C438145:ASI3 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; C082461:UBC6 protein, S cerevisiae; C077072:UBC7 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes