title: The Cdc42 GTPase-associated proteins Gic1 and Gic2 are required for polarized cell growth in Saccharomyces cerevisiae.
abstract: BEM2 of Saccharomyces cerevisiae encodes a Rho-type GTPase-activating protein that is required for proper bud site selection at 26 degrees C and for bud emergence at elevated temperatures. We show here that the temperature-sensitive growth phenotype of bem2 mutant cells can be suppressed by increased dosage of the GIC1 gene. The Gic1 protein, together with its structural homolog Gic2, are required for cell size and shape control, bud site selection, bud emergence, actin cytoskeletal organization, mitotic spindle orientation/positioning, and mating projection formation in response to mating pheromone. Each protein contains a CRIB (Cdc42/Rac-interactive binding) motif and each interacts in the two-hybrid assay with the GTP-bound form of the Rho-type Cdc42 GTPase, a key regulator of polarized growth in yeast. The CRIB motif of Gic1 and the effector domain of Cdc42 are required for this association. Genetic experiments indicate that Gic1 and Gic2 play positive roles in the Cdc42 signal transduction pathway, probably as effectors of Cdc42. Subcellular localization studies with a functional green fluorescent protein-Gic1 fusion protein indicate that this protein is concentrated at the incipient bud site of unbudded cells, at the bud tip and mother-bud neck of budded cells, and at cortical sites on large-budded cells that may delimit future bud sites in the two progeny cells. The ability of Gic1 to associate with Cdc42 is important for its function but is apparently not essential for its subcellular localization.
authors.affiliation: Department of Microbiology, The University of Texas, Austin, Texas 78712, USA.
authors.forename: G C
authors.initials: GC
authors.lastname: Chen
authors.forename: Y J
authors.initials: YJ
authors.lastname: Kim
authors.forename: C S
authors.initials: CS
authors.lastname: Chan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000502:physiology*; D002451:Cell Compartmentation; D018797:Cell Cycle Proteins / Q000502:physiology*; D002455:Cell Division; D002470:Cell Survival; D005656:Fungal Proteins / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D020690:GTPase-Activating Proteins; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C084219:BEM2 protein, S cerevisiae; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; C109252:GIC1 protein, S cerevisiae; C109253:GIC2 protein, S cerevisiae; D020690:GTPase-Activating Proteins; D029701:Saccharomyces cerevisiae Proteins; C095212:CLA4 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D019204:GTP-Binding Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae