title: Regulation of cell separation in the dimorphic fungus Ustilago maydis.
abstract: During its haploid phase the dimorphic fungus Ustilago maydis grows vegetatively by budding. We have identified two genes, don1 and don3, which control the separation of mother and daughter cells. Mutant cells form tree-like clusters in liquid culture and grow as ring-like (donut-shaped) colonies on solid medium. In wild-type U. maydis cells, two distinct septa are formed during cytokinesis and delimit a fragmentation zone. Cells defective for either don1 or don3 display only a single septum and fail to complete cell separation. don1 encodes a guanine nucleotide exchange factor (GEF) of the Dbl family specific for Rho/Rac GTPases. Don3 belongs to the germinal-centre-kinase (GC) subfamily of Ste20-like protein kinases. We have isolated the U. maydis homologues of the small GTP binding proteins Rho2, Rho3, Rac1 and Cdc42. Out of these, only Cdc42 interacts specifically with Don1 and Don3 in the yeast two-hybrid system. We propose that Don1 and Don3 regulate the initiation of the secondary septum, which is required for proper cell separation.
authors.affiliation: Institut für Genetik der Universität München, Munich, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Weinzierl
authors.forename: Leonora
authors.initials: L
authors.lastname: Leveleki
authors.forename: Annette
authors.initials: A
authors.lastname: Hassel
authors.forename: Gerhard
authors.initials: G
authors.lastname: Kost
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wanner
authors.forename: Michael
authors.initials: M
authors.lastname: Bölker
mesh_terms: D000595:Amino Acid Sequence; D002455:Cell Division; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D020930:MAP Kinase Kinase Kinases; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D020798:Two-Hybrid System Techniques; D014588:Ustilago / Q000166:cytology* / Q000235:genetics / Q000378:metabolism; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; D020930:MAP Kinase Kinase Kinases; C078754:STE20 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae