View the Current Issue

Article

  • The EMBO Journal (2007) 26, 3296 - 3307
  • doi:10.1038/sj.emboj.7601775

Published online: 28 June 2007

The Caenorhabditis elegans septin complex is nonpolar

Corinne M John1,ab, Richard K Hite2,a, Christine S Weirich1,a, Daniel J Fitzgerald3,b, Hatim Jawhari4,c, Mahamadou Faty1,d, Dominik Schläpfer1, Ruth Kroschewski1, Fritz K Winkler4, Tom Walz2, Yves Barral1 and Michel O Steinmetz4

  1. Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
  2. Department of Cell Biology, Harvard Medical School, Boston, MA, USA
  3. Institute of Molecular Biology and Biophysics, ETH Zürich, Zürich, Switzerland
  4. Biomolecular Research, Structural Biology, Paul Scherrer Institut, Villigen, Switzerland

Correspondence to:

Yves Barral, Institute of Biochemistry, ETH Zürich, 8093 Zürich, Switzerland. Tel.: +41 44 632 0678; Fax: +41 44 632 1591; E-mail: yves.barral@bc.biol.ethz.ch

aThese authors contributed equally to this study

bPresent address: Redbiotec AG, Wagistrasse 23, 8952 Schlieren, Switzerland

cPresent address: Actelion Pharmaceuticals Ltd, Gewerbestrasse 16, 4123 Allschwil, Switzerland

dPresent address: Friedrich-Miescher-Institute, WRO 1066-P46, Maulbeerstrasse 66, 4058 Basel, Switzerland

Received 30 April 2007; Accepted 25 May 2007

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.

  • Keywords:

    • cell polarity,
    • coiled coil,
    • cytoskeleton,
    • electron microscopy,
    • septin