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J. Biol. Chem., Vol. 283, Issue 35, 23872-23883, August 29, 2008

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The Cytokinesis Formins from the Nematode Worm and Fission Yeast Differentially Mediate Actin Filament Assembly^*

Erin M. Neidt, Colleen T. Skau, and David R. Kovar¹

From the Departments of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637

Formins drive actin filament assembly for diverse cellular processes including motility, establishing polarity, and cell division. To investigate the mechanism of contractile ring assembly in animal cells, we directly compared the actin assembly properties of formins required for cytokinesis in the nematode worm early embryo (CYK-1) and fission yeast (Cdc12p). Like Cdc12p and most other formins, CYK-1 nucleates actin filament assembly and remains processively associated with the elongating barbed end while facilitating the addition of profilin-actin above the theoretical diffusion-limited rate. However, specific properties differ significantly between Cdc12p and CYK-1. Cdc12p efficiently nucleates filaments that in the presence of profilin elongate at approximately the same rate as control filaments without formin (10.0 subunits/s). CYK-1 is an inefficient nucleator but allows filaments to elongate profilin-actin 6-fold faster than Cdc12p (60 subunits/s). Both Cdc12p and CYK-1 bind to pre-assembled actin filaments with low nanomolar affinity, but CYK-1 dissociates 2 orders of magnitude more quickly. However, CYK-1 rapidly re-associates with free barbed ends. Cdc12p allows barbed ends to elongate in the presence of excess capping protein, whereas capping protein inhibits CYK-1-mediated actin assembly. Therefore, these evolutionarily diverse formins can drive contractile ring assembly by a generally similar mechanism, but cells with unique dimensions and physical parameters might require proteins with carefully tuned actin assembly properties.

Received for publication, May 15, 2008 , and in revised form, June 18, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grant GM-079265. This work was also supported by an Edward Mallinckrodt, Jr. Foundation grant and a Cancer Research Foundation grant (to D. R. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: 920 East 58th St., Suite 915 E, Chicago, IL 60637. Fax: 773-702-3172; E-mail: drkovar{at}uchicago.edu.

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