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A more recent version of this article appeared on December 1, 2004
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Submitted on July 28, 2004
Accepted on September 9, 2004

*Howard Hughes Medical Institute,
Department of Cell and Developmental Biology, and
Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232
Monitoring Editor: Trisha Davis
Septins are GTP binding proteins important for cytokinesis in many eukaryotes. The Schizosaccaromyces pombe genome sequence predicts orthologues of four of five S. cerevisiae septins involved in cytokinesis and these are named Spns1-4p. That spns1-4 are not essential genes permitted the application of a combined genetic and proteomics approach to determine their functional relationships. Our findings indicate that Spns1-4p are present throughout interphase as a diffusely localized
8.5S complex containing two copies of each septin linked together as a chain in the order Spn3p-Spn4p-Spn1p-Spn2p. Septin recruitment to the medial region of the cell is genetically separable from ring formation and while it is normally restricted to mitosis, it can be promoted without activation of the mitotic cell cycle machinery. Coalescence into ring structures requires Spn1p and Spn4p associate with at least one other septin subunit and the expression of Mid2p that is normally restricted to mitosis. This study establishes the functional requirements for septin complex organization in vivo.
Corresponding author.
E-mail: kathy.gould{at}vanderbilt.edu