title: Lack of GTP-bound Rho1p in secretory vesicles of Saccharomyces cerevisiae.
abstract: Rho1p, an essential Rho-type GTPase in Saccharomyces cerevisiae, activates its effectors in the GTP-bound form. Here, we show that Rho1p in secretory vesicles cannot activate 1,3-beta-glucan synthase, a cell wall synthesizing enzyme, during vesicular transport to the plasma membrane. Analyses with an antibody preferentially reacting with the GTP-bound form of Rho1p revealed that Rho1p remains in the inactive form in secretory vesicles. Rom2p, the GDP/GTP exchange factor of Rho1p, is preferentially localized on the plasma membrane even when vesicular transport is blocked. Overexpression of Rom2p results in delocalization of Rom2p and accumulation of 1,3-beta-glucan in secretory vesicles. Based on these results, we propose that Rho1p is kept inactive in intracellular secretory organelles, resulting in repression of the activity of the cell wall-synthesizing enzyme within cells.
authors.affiliation: Dept. of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, FSB-101, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Abe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Qadota
authors.forename: Aiko
authors.initials: A
authors.lastname: Hirata
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ohya
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005057:Eukaryotic Cells / Q000201:enzymology* / Q000648:ultrastructure; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism*; D008565:Membrane Proteins; D009154:Mutation / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D047071:beta-Glucans; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000906:Antibodies; D004268:DNA-Binding Proteins; D005936:Glucans; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D010940:Plant Proteins; C490929:ROM2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D047071:beta-Glucans; D006160:Guanosine Triphosphate; C033363:beta-1,3-glucan; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase; C051302:RHO1 protein, S cerevisiae; D020741:rho GTP-Binding Proteins; C511156:rho1 protein, S pombe