title: C-terminal anchoring of mid1p to membranes stabilizes cytokinetic ring position in early mitosis in fission yeast.
abstract: mid1p is a key factor for the central positioning of the cytokinetic ring in Schizosaccharomyces pombe. In interphase and early mitosis, mid1p forms a medial cortical band overlying the nucleus, which may represent a landmark for cytokinetic ring assembly. It compacts before anaphase into a tight ring with other cytokinetic ring components. We show here that mid1p binds to the medial cortex by at least two independent means. First, mid1p C-terminus association with the cortex requires a putative amphipathic helix adjacent to mid1p nuclear localization sequence (NLS), which is predicted to insert directly into the lipid bilayer. This association is stabilized by the polybasic NLS. mid1p mutated within the helix and the NLS forms abnormal filaments in early mitosis that are not properly anchored to the medial cortex. Misplaced rings assemble in late mitosis, indicating that mid1p C-terminus binding to membranes stabilizes cytokinetic ring position. Second, the N terminus of mid1p has the ability to associate faintly with the medial cortex and is sufficient to form tight rings. In addition, we show that mid1p oligomerizes. We propose that membrane-bound oligomers of mid1p assemble recruitment "platforms" for cytokinetic ring components at the medial cortex and stabilize the ring position during its compaction.
authors.affiliation: UMR144 CNRS-Institut Curie, 26 rue d'Ulm, 75248 Paris Cedex 05, France.
authors.forename: Séverine
authors.initials: S
authors.lastname: Celton-Morizur
authors.forename: Nicole
authors.initials: N
authors.lastname: Bordes
authors.forename: Vincent
authors.initials: V
authors.lastname: Fraisier
authors.forename: Phong T
authors.initials: PT
authors.lastname: Tran
authors.forename: Anne
authors.initials: A
authors.lastname: Paoletti
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000737:chemistry; D048749:Cytokinesis; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D008566:Membranes / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D008938:Mitosis; D008954:Models, Biological; D009154:Mutation; D019913:Nuclear Localization Signals; D038761:Photobleaching; D011233:Precipitin Tests; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D005656:Fungal Proteins; D008051:Lipid Bilayers; C489694:Mid1 protein, S pombe; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; D005982:Glutathione Transferase