Gong T, Liao Y, He F, Yang Y, Yang DD, Chen XD, Gao XD

In the budding yeast Saccharomyces cerevisiae, Rho4 GTPase partially plays a redundant role with Rho3 in the control of polarized growth as deletion of RHO4 and RHO3 together, but not RHO4 alone, caused lethality and a loss of cell polarity at 30°C. Here, we show that overexpression of constitutively active ...

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rho4(Q131L) mutant in an rdi1Δ strain caused a severe growth defect and generated large, round, unbudded cells, suggesting that an excess of Rho4 activity could block bud emergence. We also generated four temperature-sensitive rho4-Ts alleles in a rho3Δ rho4Δ strain. These mutants showed growth and morphological defects at 37°C. Interestingly, two rho4-Ts alleles contain mutations that cause amino acid substitutions in the N-terminal region of Rho4. Rho4 possesses a long N-terminal extension that is unique among the six Rho GTPases in the budding yeast but is common in Rho4 homologs in other yeasts and filamentous fungi. We show that the N-terminal extension plays an important role in Rho4 function since rho3Δ rho4(Δ)(61) cells expressing truncated Rho4 lacking region 1-61 a.a. exhibited morphological defects at 24°C and a growth defect at 37°C. Furthermore, we show that Rho4 interacts with Bem2, a RhoGAP for Cdc42 and Rho1, by yeast two-hybrid, BiFC, and GST pull-down assays. Bem2 specifically interacts with the GTP-bound form of Rho4 and the interaction is mediated by its RhoGAP domain. Overexpression of BEM2 aggravates the defects of rho3Δ rho4 mutants. These results suggest that Bem2 might be a novel GAP for Rho4.

Date: Dec. 21, 2012

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