Genetics. Published Articles Ahead of Print: October 8, 2006, Copyright © 2006
doi:10.1534/genetics.106.059154


A more recent version of this article appeared on December 1, 2006.

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The Cdc34/SCF ubiquitination complex mediates Saccharomyces cerevisiae cell wall integrity

Xaralabos Varelas 1, David T Stuart 2, Michael J Ellison 2* and Christopher Ptak 2

1 Samuel Lunenfeld Research Institute, Mount Sinai Hospital
2 University of Alberta

* To whom correspondence should be addressed. E-mail: mike.ellison{at}ualberta.ca.

Submitted on April 7, 2006
Revised on May 15, 2006
Accepted on 13 September 2006


Abstract

To identify novel functions for the Cdc34/SCF ubiquitination complex we analyzed genome-wide transcriptional profiles of cdc53-1 and cdc34-2 Saccharomyces cerevisiae mutants. This analysis revealed altered expression for several gene families, including genes involved in the regulation of cell wall organization and biosynthesis. This led us to uncover a role for the Cdc34/SCF complex in the regulation of cell wall integrity. In support of this, cdc53-1 and cdc34-2 mutants exhibit phenotypes characteristic of cell wall integrity mutants, such as SDS sensitivity and temperature sensitive suppression by osmotic stabilizers. Examination of these mutants revealed defects in their induction of Slt2 phosphorylation, indicating defects in Pkc1-Slt2 MAPK signaling. Consistent with this, synthetic genetic interactions were observed between the genes encoding the Cdc34/SCF complex and key components of the Pck1-Slt2 MAPK pathway. Further analysis revealed that Cdc34/SCF mutants have reduced levels of active Rho1, suggesting that these defects stem from the deregulated activity of the Rho1 GTPase. Altering the activity of Rho1 via manipulation of the Rho1-GAPs LRG1 or SAC7 affected Cdc34/SCF mutant growth. Strikingly, however, deletion of LRG1 rescued the growth defects associated with Cdc34/SCF mutants, whereas deletion of SAC7 enhanced these defects. Given the differential roles that these GAPs play in the regulation of Rho1, these observations indicate the importance of coordinating Cdc34/SCF activity with specific Rho1 functions.

Key Words: Cdc34, Cdc53, Rho1, cell integrity, ubiquitin