title: Lrg1p Is a Rho1 GTPase-activating protein required for efficient cell fusion in yeast.
abstract: 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.
authors.affiliation: The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Pamela G
authors.initials: PG
authors.lastname: Fitch
authors.forename: Alison E
authors.initials: AE
authors.lastname: Gammie
authors.forename: Debbie J
authors.initials: DJ
authors.lastname: Lee
authors.forename: Valeria Brizzio
authors.initials: VB
authors.lastname: de Candal
authors.forename: Mark D
authors.initials: MD
authors.lastname: Rose
mesh_terms: 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
chemical_list: 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