Lrg1p Is a Rho1 GTPase-activating protein required for efficient cell fusion in yeast.
To identify additional cell fusion genes in Saccharomyces cerevisiae, we performed a high-copy suppressor screen of fus2Delta. Higher dosage of three genes, BEM1, LRG1, and FUS1, partially suppressed the fus2Delta cell fusion defect. BEM1 and FUS1 were high-copy suppressors of many cell-fusion-defective mutations, whereas LRG1 suppressed only fus2Delta and rvs161Delta. 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 fus2Delta. Furthermore, lrg1Delta 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 beta(1-3)-glucan synthase in vitro. beta(1-3)-glucan deposition was increased in lrg1Delta strains and mislocalized to the tip of the mating projection in fus2Delta strains. High-copy LRG1 suppressed the mislocalization of beta(1-3) glucan in fus2Delta 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.
Fitch
Pamela G
PG
The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA.
Gammie
Alison E
AE
Lee
Debbie J
DJ
de Candal
Valeria Brizzio
VB
Rose
Mark D
MD
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D002450:Cell Communication; D002459:Cell Fusion; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D008565:Membrane Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D047071:beta-Glucans / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C490024:FUS1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; C088938:LRG1 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D047071:beta-Glucans; C085379:rho GTPase-activating protein; C073129:BEM1 protein, S cerevisiae; C033363:beta-1,3-glucan