title: Gef1p, a new guanine nucleotide exchange factor for Cdc42p, regulates polarity in Schizosaccharomyces pombe.
abstract: Schizosaccharomyces pombe cdc42(+) regulates cell morphology and polarization of the actin cytoskeleton. Scd1p/Ral1p is the only described guanine nucleotide exchange factor (GEF) for Cdc42p in S. pombe. We have identified a new GEF, named Gef1p, specifically regulating Cdc42p. Gef1p binds to inactive Cdc42p but not to other Rho GTPases in two-hybrid assays. Overexpression of gef1(+) increases specifically the GTP-bound Cdc42p, and Gef1p is capable of stimulating guanine nucleotide exchange of Cdc42p in vitro. Overexpression of gef1(+) causes changes in cell morphology similar to those caused by overexpression of the constitutively active cdc42G12V allele. Gef1p localizes to the septum. gef1(+) deletion is viable but causes a mild cell elongation and defects in bipolar growth and septum formation, suggesting a role for Gef1p in the control of cell polarity and cytokinesis. The double mutant gef1delta scd1delta is not viable, indicating that they share an essential function as Cdc42p activators. However, both deletion and overexpression of either gef1(+) or scd1(+) causes different morphological phenotypes, which suggest different functions. Genetic evidence revealed a link between Gef1p and the signaling pathway of Shk1/Orb2p and Orb6p. In contrast, no genetic interaction between Gef1p and Shk2p-Mkh1p pathway was observed.
authors.affiliation: Instituto de Microbiología Bioquímica, Consejo Superior de Investigaciones Científicas/Departamento de Microbiologia y Genetica, Universidad de Salamanca, Edificio Departamental, 37007 Salamanca, Spain.
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Coll
authors.forename: Yadira
authors.initials: Y
authors.lastname: Trillo
authors.forename: Amagoia
authors.initials: A
authors.lastname: Ametzazurra
authors.forename: Pilar
authors.initials: P
authors.lastname: Perez
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D011518:Proto-Oncogene Proteins; D029702:Schizosaccharomyces pombe Proteins; C089769:scd1 protein, S pombe; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D020764:cdc42 GTP-Binding Protein