Targeting of Nbp1 to the inner nuclear membrane is essential for spindle pole body duplication |
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Authors: | Kupke Thomas Di Cecco Leontina Müller Hans-Michael Neuner Annett Adolf Frank Wieland Felix Nickel Walter Schiebel Elmar |
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Affiliation: | 1.Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany;2.Biochemie-Zentrum der Universität Heidelberg (BZH), Heidelberg, Germany |
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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. |
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Keywords: | amphipathic helix in‐plane membrane anchor Kap123 Nbp1 spindle pole body duplication |
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