title: Targeting of Nbp1 to the inner nuclear membrane is essential for spindle pole body duplication.
abstract: Spindle pole bodies (SPBs), like nuclear pore complexes, are embedded in the nuclear envelope (NE) at sites of fusion of the inner and outer nuclear membranes. A network of interacting proteins is required to insert a cytoplasmic SPB precursor into the NE. A central player of this network is Nbp1 that interacts with the conserved integral membrane protein Ndc1. Here, we establish that Nbp1 is a monotopic membrane protein that is essential for SPB insertion at the inner face of the NE. In vitro and in vivo studies identified an N-terminal amphipathic α-helix of Nbp1 as a membrane-binding element, with crucial functions in SPB duplication. The karyopherin Kap123 binds to a nuclear localization sequence next to this amphipathic α-helix and prevents unspecific tethering of Nbp1 to membranes. After transport into the nucleus, Nbp1 binds to the inner nuclear membrane. These data define the targeting pathway of a SPB component and suggest that the amphipathic α-helix of Nbp1 is important for SPB insertion into the NE from within the nucleus.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kupke
authors.forename: Leontina
authors.initials: L
authors.lastname: Di Cecco
authors.forename: Hans-Michael
authors.initials: HM
authors.lastname: Müller
authors.forename: Annett
authors.initials: A
authors.lastname: Neuner
authors.forename: Frank
authors.initials: F
authors.lastname: Adolf
authors.forename: Felix
authors.initials: F
authors.lastname: Wieland
authors.forename: Walter
authors.initials: W
authors.lastname: Nickel
authors.forename: Elmar
authors.initials: E
authors.lastname: Schiebel
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017384:Sequence Deletion; D008941:Spindle Apparatus / Q000378:metabolism*; D013329:Structure-Activity Relationship; D028961:beta Karyopherins / Q000235:genetics / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C109173:Kap123 protein, S cerevisiae; D008081:Liposomes; C408226:NBP1 protein, S cerevisiae; C082594:NDC1 protein, S cerevisiae; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D010713:Phosphatidylcholines; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D028961:beta Karyopherins