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Vol. 18, Issue 10, 4155-4167, October 2007

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Regulation of the Formin for3p by cdc42p and bud6p

Sophie G. Martin^*,, Sergio A. Rincón, Roshni Basu^*, Pilar Pérez, and Fred Chang^*

*Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, NY 10032; and Instituto de Microbiología Bioquímica, Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, 37007 Salamanca, Spain

Submitted February 2, 2007; Revised July 31, 2007; Accepted August 3, 2007
Monitoring Editor: Thomas Pollard

Formins are conserved actin nucleators responsible for the assembly of diverse actin structures. Many formins are controlled through an autoinhibitory mechanism involving the interaction of a C-terminal DAD sequence with an N-terminal DID sequence. Here, we show that the fission yeast formin for3p, which mediates actin cable assembly and polarized cell growth, is regulated by a similar autoinhibitory mechanism in vivo. Multiple sites govern for3p localization to cell tips. The localization and activity of for3p are inhibited by an intramolecular interaction of divergent DAD and DID-like sequences. A for3p DAD mutant expressed at endogenous levels produces more robust actin cables, which appear to have normal organization and dynamics. We identify cdc42p as the primary Rho GTPase involved in actin cable assembly and for3p regulation. Both cdc42p, which binds at the N terminus of for3p, and bud6p, which binds near the C-terminal DAD-like sequence, are needed for for3p localization and full activity, but a mutation in the for3p DAD restores for3p localization and other phenotypes of cdc42 and bud6 mutants. In particular, the for3p DAD mutation suppresses the bipolar growth (NETO) defect of bud6 cells. These findings suggest that cdc42p and bud6p activate for3p by relieving autoinhibition.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Center for Integrative Genomics, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland.

Address correspondence to: Fred Chang (fc99{at}columbia.edu)

Abbreviations used: DAD, Diaphanous Autoregulatory Domain; DID, Diaphanous Inhibitory Domain; FH, Formin Homology; LatA, Latrunculin A; NETO, New End Take Off.

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