title: Dissection of mitotic functions of the yeast cyclin Clb2.
abstract: Progression through mitosis requires the activity of cyclin-dependent kinases (CDKs) associated with regulatory cyclin subunits. In the yeast Saccharomyces cerevisiae, Clb2 has the most important role among the four mitotic cyclins, Clb1-4, manifested by data showing that simultaneous deletion of the CLB1, CLB3 and CLB4 genes has only minor effects on mitosis. Thus, Clb2 alone is sufficient for all essential CDK functions in mitosis, such as the assembly of bipolar spindles and spindle elongation. Here, we show that a modification of Clb2, by the C-terminal addition of a Myc12 epitope, causes the loss of one specific mitotic function of Clb2. Strains carrying CLB2-MYC12 are nonviable in the absence of the CLB3 and CLB4 genes, because the modified Clb2 version fails to promote assembly of the mitotic spindle. In contrast, Clb2-Myc12 has no apparent defects in late mitotic functions and, furthermore, induces the switch from polarized to isotropic growth with similar efficiency as the endogenous Clb2. Thus, the presence of the Myc12 epitope selectively inactivates Clb2's capacity to promote spindle formation. Clb2-Myc12 represents therefore the first version of Clb2 impaired in one specific mitotic function. We conclude that the major mitotic functions of this cyclin can be unequivocally dissected.
authors.affiliation: Institute of Microbiology and Genetics, Georg August University, Göttingen, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Kuczera
authors.forename: Özgür
authors.initials: Ö
authors.lastname: Bayram
authors.forename: Fatih
authors.initials: F
authors.lastname: Sari
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Braus
authors.forename: Stefan
authors.initials: S
authors.lastname: Irniger
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism*; D000939:Epitopes / Q000276:immunology; D017353:Gene Deletion; D005800:Genes, Fungal / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000378:metabolism; D050296:Microbial Viability; D008938:Mitosis; D009154:Mutation / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism
chemical_list: C093749:CLB2 protein, S cerevisiae; D019926:Cyclin B; D000939:Epitopes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins