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Mol Biol Cell. 2008 Apr;19(4):1763-71. doi: 10.1091/mbc.E07-09-0950. Epub 2008 Feb 6.

G1/S cyclin-dependent kinase regulates small GTPase Rho1p through phosphorylation of RhoGEF Tus1p in Saccharomyces cerevisiae.

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Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Chiba 277-8562, Japan.


Rho1p is an essential small GTPase that plays a key role in the morphogenesis of Saccharomyces cerevisiae. We show here that the activation of Rho1p is regulated by a cyclin-dependent kinase (CDK). Rho1p is activated at the G1/S transition at the incipient-bud sites by the Cln2p (G1 cyclin) and Cdc28p (CDK) complex, in a process mediated by Tus1p, a guanine nucleotide exchange factor for Rho1p. Tus1p interacts physically with Cln2p/Cdc28p and is phosphorylated in a Cln2p/Cdc28p-dependent manner. CDK phosphorylation consensus sites in Tus1p are required for both Cln2p-dependent activation of Rho1p and polarized organization of the actin cytoskeleton. We propose that Cln2p/Cdc28p-dependent phosphorylation of Tus1p is required for appropriate temporal and spatial activation of Rho1p at the G1/S transition.

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