title: Cdc55p, the B-type regulatory subunit of protein phosphatase 2A, has multiple functions in mitosis and is required for the kinetochore/spindle checkpoint in Saccharomyces cerevisiae.
abstract: Saccharomyces cerevisiae, like most eucaryotic cells, can prevent the onset of anaphase until chromosomes are properly aligned on the mitotic spindle. We determined that Cdc55p (regulatory B subunit of protein phosphatase 2A [PP2A]) is required for the kinetochore/spindle checkpoint regulatory pathway in yeast. ctf13 cdc55 double mutants could not maintain a ctf13-induced mitotic delay, as determined by antitubulin staining and levels of histone H1 kinase activity. In addition, cdc55::LEU2 mutants and tpd3::LEU2 mutants (regulatory A subunit of PP2A) were nocodazole sensitive and exhibited the phenotypes of previously identified kinetochore/spindle checkpoint mutants. Inactivating CDC55 did not simply bypass the arrest that results from inhibiting ubiquitin-dependent proteolysis because cdc16-1 cdc55::LEU2 and cdc23-1 cdc55::LEU2 double mutants arrested normally at elevated temperatures. CDC55 is specific for the kinetochore/spindle checkpoint because cdc55 mutants showed normal sensitivity to gamma radiation and hydroxyurea. The conditional lethality and the abnormal cellular morphogenesis of cdc55::LEU2 were suppressed by cdc28F19, suggesting that the cdc55 phenotypes are dependent on the phosphorylation state of Cdc28p. In contrast, the nocodazole sensitivity of cdc55::LEU2 was not suppressed by cdc28F19. Therefore, the mitotic checkpoint activity of CDC55 (and TPD3) is independent of regulated phosphorylation of Cdc28p. Finally, cdc55::LEU2 suppresses the temperature sensitivity of cdc20-1, suggesting additional roles for CDC55 in mitosis.
authors.affiliation: Department of Biology, University of Virginia, Charlottesville 22903, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: D J
authors.initials: DJ
authors.lastname: Burke
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004249:DNA Damage; D004271:DNA, Fungal / Q000096:biosynthesis; D005656:Fungal Proteins / Q000235:genetics; D005720:Gamma Rays; D005816:Genetic Complementation Test; D006918:Hydroxyurea / Q000494:pharmacology; D018386:Kinetochores / Q000502:physiology*; D008870:Microtubules / Q000187:drug effects; D008938:Mitosis / Q000502:physiology*; D009154:Mutation; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins / Q000235:genetics; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D006656:Protamine Kinase / Q000378:metabolism; D054648:Protein Phosphatase 2; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins; D008941:Spindle Apparatus / Q000502:physiology; D013172:Spores, Fungal; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: C071246:CDC55 protein, S cerevisiae; C081354:CTF13 protein, S cerevisiae; D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D006656:Protamine Kinase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D015739:Nocodazole; D006918:Hydroxyurea