title: Inhibition of APC-mediated proteolysis by the meiosis-specific protein kinase Ime2.
abstract: Proteolysis triggered by the anaphase-promoting complex (APC) is needed for sister chromatid separation and the exit from mitosis. APC is a ubiquitin ligase whose activity is tightly controlled during the cell cycle. To identify factors involved in the regulation of APC-mediated proteolysis, a Saccharomyces cerevisiae GAL-cDNA library was screened for genes whose overexpression prevented degradation of an APC target protein, the mitotic cyclin Clb2. Genes encoding G1, S, and mitotic cyclins were identified, consistent with previous data showing that the cyclin-dependent kinase Cdk1 associated with different cyclins is a key factor for inhibiting APC(Cdh1) activity from late-G1 phase until mitosis. In addition, the meiosis-specific protein kinase Ime2 was identified as a negative regulator of APC-mediated proteolysis. Ectopic expression of IME2 in G1 arrested cells inhibited the degradation of mitotic cyclins and of other APC substrates. IME2 expression resulted in the phosphorylation of Cdh1 in G1 cells, indicating that Ime2 and Cdk1 regulate APC(Cdh1) in a similar manner. The expression of IME2 in cycling cells inhibited bud formation and caused cells to arrest in mitosis. We show further that Ime2 itself is an unstable protein whose proteolysis occurs independently of the APC and SCF (Skp1/Cdc53/F-box) ubiquitin ligases. Our findings suggest that Ime2 represents an unstable, meiosis-specific regulator of APC(Cdh1).
authors.affiliation: Institute of Microbiology and Genetics, Georg-August-University, Grisebachstrasse 8, D-37077 Göttingen, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Bolte
authors.forename: Patrick
authors.initials: P
authors.lastname: Steigemann
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Braus
authors.forename: Stefan
authors.initials: S
authors.lastname: Irniger
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication; D018076:DNA, Complementary / Q000032:analysis; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D016193:G1 Phase; D047908:Intracellular Signaling Peptides and Proteins; D008025:Ligases / Q000037:antagonists & inhibitors / Q000502:physiology*; D008540:Meiosis; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D064249:Securin; D043743:Ubiquitin-Protein Ligase Complexes
chemical_list: C577583:CDH1 protein, S cerevisiae; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins; D018076:DNA, Complementary; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; C578004:PDS1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D064249:Securin; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D011494:Protein Kinases; C064979:IME2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C081927:CDC5 protein, S cerevisiae; D008025:Ligases