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Vol. 21, Issue 3, 430-442, February 1, 2010

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Membrane Trafficking

The Exo70 Subunit of the Exocyst Is an Effector for Both Cdc42 and Rho3 Function in Polarized Exocytosis

Hao Wu^*, Courtney Turner^*, Jimmy Gardner^*, Brenda Temple, and Patrick Brennwald^*

Departments of *Cell and Developmental Biology and Biochemistry and Biophysics and R. L. Juliano Structural Bioinformatics Core, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090

Submitted June 18, 2009; Revised November 20, 2009; Accepted November 23, 2009
Monitoring Editor: Sean Munro

The Rho3 and Cdc42 members of the Rho GTPase family are important regulators of exocytosis in yeast. However, the precise mechanism by which they regulate this process is controversial. Here, we present evidence that the Exo70 component of the exocyst complex is a direct effector of both Rho3 and Cdc42. We identify gain-of-function mutants in EXO70 that potently suppress mutants in RHO3 and CDC42 defective for exocytic function. We show that Exo70 has the biochemical properties expected of a direct effector for both Rho3 and Cdc42. Surprisingly, we find that C-terminal prenylation of these GTPases both promotes the interaction and influences the sites of binding within Exo70. Finally, we demonstrate that the phenotypes associated with novel loss-of-function mutants in EXO70, are entirely consistent with Exo70 as an effector for both Rho3 and Cdc42 function in secretion. These data suggest that interaction with the Exo70 component of the exocyst is a key event in spatial regulation of exocytosis by Rho GTPases.

Address correspondence to: Patrick Brennwald (pjbrennw{at}med.unc.edu)