Regulation of Cell Polarity in Saccharomyces cerevisiae by
Gpa1 and Fus3.
Metodi Metodiev, Sofia Zaichick, Hye-Jin
Kim, David Stone
Biological Sciences, LMB, U of Illinois at Chicago,
900 S. Ashland, Chicago, IL 60607, USA
We have shown that Gpa1, the
mating specific G-alpha protein of S. cerevisiae, interacts
directly with the mating-specific MAPK (Fus3) during mating. A K21E R22E
mutation in the putative MAPK docking site of Gpa1 decreased the Gpa1-Fus3 interaction, and abolished the hyperadaptive function of
Gpa1E364K. gpa1K21E R22E conferred slight
supersensitivity to pheromone, decreased mating efficiency 15-fold, and
compromised the chemotropic response (Metodiev et al. Science, in
press). Further studies revealed that the docking site mutation in G-alpha also causes a defect in polarization, nuclear migration, and a
dramatic change in microtubule organization during mating.
Interestingly, a proteomic screen identified Kar3 as a protein that
associates with GST-Gpa1 in cells treated with pheromone. Kar3 is a
microtubule motor protein essential for nuclear movement and karyogamy.
It contains a canonical MAPK phosphorylation motif (PRTP) at its N-terminus, and is therefore a potential target for Fus3. Together, our
results suggest that Gpa1 and Fus3 regulate nuclear migration during
mating via Kar3 and microtubule dynamics. A model of this pathway will
be discussed.
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