title: The guanine-nucleotide-exchange factor Cdc24p is targeted to the nucleus and polarized growth sites.
abstract: Generation of cellular asymmetry or cell polarity plays a critical role in cell-cycle-regulated morphogenetic processes involving the actin cytoskeleton. The GTPase Cdc42 regulates actin rearrangements and signal transduction pathways in all eukaryotic cells [1], and the temporal and spatial regulation of Cdc42p depends on the activity and targeting of its guanine-nucleotide exchange factor (GEF). Cdc24p, the Saccharomyces cerevisiae GEF for Cdc42p, is found in a particulate fraction and localizes to the plasma membrane [2] [3] at sites of polarized growth [4]. We show that Cdc24p labeled with green fluorescent protein (GFP-Cdc24p) was targeted to pre-bud sites, the tips and sides of enlarging buds, and mating projections in pheromone-treated cells. Unexpectedly, GFP-Cdc24p also localized to the nucleus and GFP-Cdc24p levels diminished before nuclear division followed by its reappearance in divided nuclei and mother-bud necks during cytokinesis. The Cdc24p amino-terminal 283 amino acids were necessary and sufficient for nuclear localization, which depended on the cyclin-dependent-kinase inhibitor Far1p. The Cdc24p carboxy-terminal 289 amino acids were necessary and sufficient for targeting to the pre-bud site, bud, mother-bud neck, and mating projection. Targeting was independent of the Cdc24p-binding proteins Far1p, the GTPase Rsr1p/Bud1p, the scaffold protein Bem1p, and the G(beta) subunit Ste4p. These data are consistent with a temporal and spatial regulation of Cdc24p-dependent activation of Cdc42p during the cell cycle.
authors.affiliation: Department of Microbiology and Molecular Genetics, Markey Center for Molecular Genetics, The University of Vermont, Burlington, Vermont, 05405, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Toenjes
authors.forename: M M
authors.initials: MM
authors.lastname: Sawyer
authors.forename: D I
authors.initials: DI
authors.lastname: Johnson
mesh_terms: D001665:Binding Sites; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D016764:Cell Polarity; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004268:DNA-Binding Proteins / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D008164:Luminescent Proteins / Q000737:chemistry / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C073594:CDC24 protein, S cerevisiae; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D008164:Luminescent Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C086677:YAP1 protein, S cerevisiae; D049452:Green Fluorescent Proteins; D018844:Cyclin-Dependent Kinases