title: The Caenorhabditis elegans septin complex is nonpolar.
abstract: Septins are conserved GTPases that form heteromultimeric complexes and assemble into filaments that play a critical role in cell division and polarity. Results from budding and fission yeast indicate that septin complexes form around a tetrameric core. However, the molecular structure of the core and its influence on the polarity of septin complexes and filaments is poorly defined. The septin complex of the nematode Caenorhabditis elegans is formed entirely by the core septins UNC-59 and UNC-61. We show that UNC-59 and UNC-61 form a dimer of coiled-coil-mediated heterodimers. By electron microscopy, this heterotetramer appears as a linear arrangement of four densities representing the four septin subunits. Fusion of GFP to the N termini of UNC-59 and UNC-61 and subsequent electron microscopic visualization suggests that the sequence of septin subunits is UNC-59/UNC-61/UNC-61/UNC-59. Visualization of GFP extensions fused to the extremity of the C-terminal coiled coils indicates that these extend laterally from the heterotetrameric core. Together, our study establishes that the septin core complex is symmetric, and suggests that septins form nonpolar filaments.
authors.affiliation: Institute of Biochemistry, ETH Zürich, Zürich, Switzerland.
authors.forename: Corinne M
authors.initials: CM
authors.lastname: John
authors.forename: Richard K
authors.initials: RK
authors.lastname: Hite
authors.forename: Christine S
authors.initials: CS
authors.lastname: Weirich
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Fitzgerald
authors.forename: Hatim
authors.initials: H
authors.lastname: Jawhari
authors.forename: Mahamadou
authors.initials: M
authors.lastname: Faty
authors.forename: Dominik
authors.initials: D
authors.lastname: Schläpfer
authors.forename: Ruth
authors.initials: R
authors.lastname: Kroschewski
authors.forename: Fritz K
authors.initials: FK
authors.lastname: Winkler
authors.forename: Tom
authors.initials: T
authors.lastname: Walz
authors.forename: Yves
authors.initials: Y
authors.lastname: Barral
authors.forename: Michel O
authors.initials: MO
authors.lastname: Steinmetz
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism; D002850:Chromatography, Gel; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D007313:Insecta; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D015003:Yeasts
chemical_list: D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; C418245:UNC-59 protein, C elegans; C418244:unc-61 protein, C elegans; D019204:GTP-Binding Proteins