Protein-protein interactions governing septin heteropentamer assembly and septin filament organization in Saccharomyces cerevisiae.
Matthias Versele, Björn Gullbrand, Raymond Chen, Jeremy Thorner
Dept. of Molec. & Cell Biology, Univ. of California, Berkeley, Rm. 16, Barker Hall, Berkeley, CA, 94720-3202, USA
Mitotic yeast (Saccharomyces cerevisiae) cells express five related septins (Cdc3, Cdc10, Cdc11, Cdc12 and Shs1) that form a cortical filamentous collar at the mother-bud neck necessary for normal morphogenesis and cytokinesis. All five possess an N-terminal GTPase domain and, except for Cdc10, a C-terminal extension (CTE) containing a predicted coiled-coil. Here we show that the CTEs of Cdc3 and Cdc12 are essential for their association and for the function of both septins in vivo. Cdc10 interacts with a Cdc3-Cdc12 complex independently of the CTE of either protein. In contrast to Cdc3 and Cdc12, the Cdc11 CTE, which recruits the non-essential septin Shs1, is dispensable for its function in vivo. In addition, Cdc11 forms a stoichiometric complex with Cdc12, independent of its CTE. Reconstitution of various multi-septin complexes and analysis in the electron microscope reveal that Cdc3, Cdc11 and Cdc12 are all necessary and sufficient for septin filament formation, and presence of Cdc10 causes filament pairing. These data provide novel insights about the connectivity among the five individual septins in functional septin heteropentamers and the organization of septin filaments.
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