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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Active Transport, Cell Nucleus / physiology*
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Amino Acid Motifs
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Amino Acid Sequence
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Cell Cycle Proteins / chemistry
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / physiology*
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Cytoskeletal Proteins / chemistry
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Cytoskeletal Proteins / genetics
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Cytoskeletal Proteins / physiology*
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Liposomes / metabolism
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Membrane Fusion
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Molecular Sequence Data
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Nuclear Envelope / metabolism*
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Nuclear Localization Signals
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Nuclear Pore Complex Proteins / metabolism
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Nuclear Proteins / chemistry
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Nuclear Proteins / genetics
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Nuclear Proteins / physiology*
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Phosphatidylcholines / metabolism
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Protein Binding
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Protein Interaction Mapping
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Protein Structure, Secondary
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Recombinant Fusion Proteins / physiology
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Saccharomyces cerevisiae / cytology
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins / chemistry
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Saccharomyces cerevisiae Proteins / genetics
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Saccharomyces cerevisiae Proteins / metabolism
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Saccharomyces cerevisiae Proteins / physiology*
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Sequence Deletion
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Spindle Apparatus / metabolism*
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Structure-Activity Relationship
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beta Karyopherins / genetics
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beta Karyopherins / physiology*
Substances
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Cell Cycle Proteins
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Cytoskeletal Proteins
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Kap123 protein, S cerevisiae
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Liposomes
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NBP1 protein, S cerevisiae
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NDC1 protein, S cerevisiae
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Nuclear Localization Signals
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Nuclear Pore Complex Proteins
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Nuclear Proteins
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Phosphatidylcholines
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Recombinant Fusion Proteins
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Saccharomyces cerevisiae Proteins
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beta Karyopherins