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Genetics, Vol. 168, 733-746, October 2004, Copyright © 2004
doi:10.1534/genetics.104.028027
Lrg1p Is a Rho1 GTPase-Activating Protein Required for Efficient Cell Fusion in Yeast
Pamela G. Fitch*,
Alison E. Gammie
,
Debbie J. Lee
,
Valeria Brizzio de Candal
and
Mark D. Rose,1
* The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014
Harvard Medical School, Boston, Massachusetts 02115
Lifecodes Corporation, Stamford, Connecticut 06902
1 Corresponding author: Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014.
E-mail: mrose{at}molbio.princeton.edu
To identify additional cell fusion genes in Saccharomyces cerevisiae, we performed a high-copy suppressor screen of fus2
. Higher dosage of three genes, BEM1, LRG1, and FUS1, partially suppressed the fus2 cell fusion defect. BEM1 and FUS1 were high-copy suppressors of many cell-fusion-defective mutations, whereas LRG1 suppressed only fus2 and rvs161. Lrg1p contains a Rho-GAP homologous region. Complete deletion of LRG1, as well as deletion of the Rho-GAP coding region, caused decreased rates of cell fusion and diploid formation comparable to that of fus2. Furthermore, lrg1 caused a more severe mating defect in combination with other cell fusion mutations. Consistent with an involvement in cell fusion, Lrg1p localized to the tip of the mating projection. Lrg1p-GAP domain strongly and specifically stimulated the GTPase activity of Rho1p, a regulator of ß(1-3)-glucan synthase in vitro. ß(1-3)-glucan deposition was increased in lrg1 strains and mislocalized to the tip of the mating projection in fus2 strains. High-copy LRG1 suppressed the mislocalization of ß(1-3) glucan in fus2 strains. We conclude that Lrg1p is a Rho1p-GAP involved in cell fusion and speculate that it acts to locally inhibit cell wall synthesis to aid in the close apposition of the plasma membranes of mating cells.
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