title: C. elegans CUL-4 prevents rereplication by promoting the nuclear export of CDC-6 via a CKI-1-dependent pathway.
abstract: Genome stability requires that genomic DNA is replicated only once per cell cycle. The replication-licensing system ensures that the formation of prereplicative complexes is temporally separated from the initiation of DNA replication [1-4]. The replication-licensing factors Cdc6 and Cdt1 are required for the assembly of prereplicative complexes during G1 phase. During S phase, metazoan Cdt1 is targeted for degradation by the CUL4 ubiquitin ligase [5-8], and vertebrate Cdc6 is translocated from the nucleus to the cytoplasm [9, 10]. However, because residual vertebrate Cdc6 remains in the nucleus throughout S phase [10-13], it has been unclear whether Cdc6 translocation to the cytoplasm prevents rereplication [1, 2, 14]. The inactivation of C. elegans CUL-4 is associated with dramatic levels of DNA rereplication [5]. Here, we show that C. elegans CDC-6 is exported from the nucleus during S phase in response to the phosphorylation of multiple CDK sites. CUL-4 promotes the phosphorylation and subsequent translocation of CDC-6 via negative regulation of the CDK-inhibitor CKI-1. Rereplication can be induced by coexpression of nonexportable CDC-6 with nondegradable CDT-1, indicating that redundant regulation of CDC-6 and CDT-1 prevents rereplication. This demonstrates that CDC-6 translocation is critical for preventing rereplication and that CUL-4 independently controls both replication-licensing factors.
authors.affiliation: Department of Cellular Biology, University of Georgia, Athens, Georgia 30602-2607, USA.
authors.forename: Jihyun
authors.initials: J
authors.lastname: Kim
authors.forename: Hui
authors.initials: H
authors.lastname: Feng
authors.forename: Edward T
authors.initials: ET
authors.lastname: Kipreos
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology*; D042822:Genomic Instability; D008025:Ligases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D034622:RNA Interference; D016196:S Phase
chemical_list: C522445:CDC-6 protein, C elegans; D029742:Caenorhabditis elegans Proteins; C475683:Cdt-1 protein, C elegans; D018797:Cell Cycle Proteins; C475682:Cul-4 protein, C elegans; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; C115024:cki-1 protein, C elegans; D008025:Ligases