title: Triggering ubiquitination of a CDK inhibitor at origins of DNA replication.
abstract: To ensure proper timing of the G1-S transition in the cell cycle, the cyclin E-Cdk2 complex, which is responsible for the initiation of DNA replication, is restrained by the p21(Cip1)/p27(Kip1)/p57(Kip2) family of CDK (cyclin-dependent kinase) inhibitors in humans and by the related p27(Xic1) protein in Xenopus. Activation of cyclin E-Cdk2 is linked to the ubiquitination of human p27(Kip1) or Xenopus p27(Xic1) by SCF (for Skp1-Cullin-F-box protein) ubiquitin ligases. For human p27(Kip1), ubiquitination requires direct phosphorylation by cyclin E-Cdk2. We show here that Xic1 ubiquitination does not require phosphorylation by cyclin E-Cdk2, but it does require nuclear accumulation of the Xic1-cyclin E-Cdk2 complex and recruitment of this complex to chromatin by the origin-recognition complex together with Cdc6 replication preinitiation factors; it also requires an activation step necessitating cyclin E-Cdk2-kinase and SCF ubiquitin-ligase activity, and additional factors associated with mini-chromosome maintenance proteins, including the inactivation of geminin. Components of the SCF ubiquitin-ligase complex, including Skp1 and Cul1, are also recruited to chromatin through cyclin E-Cdk2 and the preinitiation complex. Thus, activation of the cyclin E-Cdk2 kinase and ubiquitin-dependent destruction of its inhibitor are spatially constrained to the site of a properly assembled preinitiation complex.
authors.affiliation: Departments of Pathology and Microbiology & Immunology, Stanford University School of Medicine, 300 Pasteur Drive, MC 5324, Palo Alto, California 94305-5324, USA.
authors.forename: L
authors.initials: L
authors.lastname: Furstenthal
authors.forename: C
authors.initials: C
authors.lastname: Swanson
authors.forename: B K
authors.initials: BK
authors.lastname: Kaiser
authors.forename: A G
authors.initials: AG
authors.lastname: Eldridge
authors.forename: P K
authors.initials: PK
authors.lastname: Jackson
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D044842:Cullin Proteins; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D005260:Female; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D051738:Origin Recognition Complex; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins; D044843:SKP Cullin F-Box Protein Ligases; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; C118388:Cdc6 protein, Xenopus; D018797:Cell Cycle Proteins; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; C100318:Cullin 1; D044842:Cullin Proteins; D019927:Cyclin E; C115373:DNA supercoiling factor, Drosophila; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D051738:Origin Recognition Complex; D044786:S-Phase Kinase-Associated Proteins; D025521:Tumor Suppressor Proteins; D014452:Ubiquitins; D029867:Xenopus Proteins; C493963:Xicl protein, Xenopus; D050760:Cyclin-Dependent Kinase Inhibitor p27; D044843:SKP Cullin F-Box Protein Ligases; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D010447:Peptide Hydrolases; D008025:Ligases; D010453:Peptide Synthases