Published 15 August 2005. doi:10.1083/jcb.200504108
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 170, Number 4, 583-594
Rho GTPase regulation of exocytosis in yeast is independent of GTP hydrolysis and polarization of the exocyst complex
Olivier Roumanie1,
Hao Wu1,
Jeffrey N. Molk2,
Guendalina Rossi1,
Kerry Bloom2, and
Patrick Brennwald1
1 Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
2 Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
Correspondence to Patrick Brennwald: pjbrennw{at}med.unc.edu
Rho GTPases are important regulators of polarity in eukaryotic cells. In yeast they are involved in regulating the docking and fusion of secretory vesicles with the cell surface. Our analysis of a Rho3 mutant that is unable to interact with the Exo70 subunit of the exocyst reveals a normal polarization of the exocyst complex as well as other polarity markers. We also find that there is no redundancy between the Rho3Exo70 and Rho1Sec3 pathways in the localization of the exocyst. This suggests that Rho3 and Cdc42 act to polarize exocytosis by activating the exocytic machinery at the membrane without the need to first recruit it to sites of polarized growth. Consistent with this model, we find that the ability of Rho3 and Cdc42 to hydrolyze GTP is not required for their role in secretion. Moreover, our analysis of the Sec3 subunit of the exocyst suggests that polarization of the exocyst may be a consequence rather than a cause of polarized exocytosis.
O. Roumanie's present address is Laboratoire de Biologie Moléculaire et Séquençage, Institut de Biochimie et Genetique Cellulaires, 33077 Bordeaux, France.
Abbreviations used in this paper: DIC, differential interference contrast; RBD, Rho-binding domain.

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