title: A lack of SUMO conjugation affects cNLS-dependent nuclear protein import in yeast.
abstract: Yeast SUMO (Smt3) and its mammalian ortholog SUMO-1 are ubiquitin-like proteins that can reversibly be conjugated to other proteins. Among the substrates for SUMO modification in vertebrates are RanGAP1 and RanBP2/Nup358, two proteins previously implicated in nucleocytoplasmic transport. Sumoylated RanGAP1 binds to the nuclear pore complex via RanBP2/Nup358, a giant nucleoporin, which was recently reported to act as a SUMO E3 ligase on some nuclear substrates. However, no direct evidence for a role of the SUMO system in nuclear transport has been obtained so far. By the use of conditional yeast mutants, we examined nuclear protein import in vivo. We show here that cNLS-dependent protein import is impaired in mutants with defective Ulp1 and Uba2, two enzymes involved in the SUMO conjugation reaction. In contrast, other transport pathways such as rgNLS-mediated protein import and mRNA export are not affected. Furthermore, we find that the yeast importin-alpha subunit Srp1 accumulates in the nucleus of ulp1 and uba2 strains but not the importin-beta subunit Kap95, indicating that a lack of Srp1 export might impair cNLS import. In summary, our results provide evidence that SUMO modification in yeast, as has been suspected for vertebrates, plays an important role in nucleocytoplasmic trafficking.
authors.affiliation: Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Strasse 10, D-13092 Berlin, Germany. kstade@mdc-berlin.de
authors.forename: Katrin
authors.initials: K
authors.lastname: Stade
authors.forename: Frank
authors.initials: F
authors.lastname: Vogel
authors.forename: Ingrid
authors.initials: I
authors.lastname: Schwienhorst
authors.forename: Birgit
authors.initials: B
authors.lastname: Meusser
authors.forename: Corinna
authors.initials: C
authors.lastname: Volkwein
authors.forename: Brigitte
authors.initials: B
authors.lastname: Nentwig
authors.forename: R Jürgen
authors.initials: RJ
authors.lastname: Dohmen
authors.forename: Thomas
authors.initials: T
authors.lastname: Sommer
mesh_terms: D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000235:genetics; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000378:metabolism; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D044764:Ubiquitin-Activating Enzymes; D015003:Yeasts / Q000502:physiology; D028901:alpha Karyopherins / Q000378:metabolism*; D028961:beta Karyopherins / Q000378:metabolism
chemical_list: C423142:KPNA1 protein, human; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D011506:Proteins; D012333:RNA, Messenger; D025841:Small Ubiquitin-Related Modifier Proteins; C470301:UBA2 protein, human; D028901:alpha Karyopherins; D028961:beta Karyopherins; D049452:Green Fluorescent Proteins; D003546:Cysteine Endopeptidases; C118083:Ulp1 protease; D044764:Ubiquitin-Activating Enzymes