title: Spatio-temporal regulation of the human licensing factor Cdc6 in replication and mitosis.
abstract: To maintain genome stability, the thousands of replication origins of mammalian genomes must only initiate replication once per cell cycle. This is achieved by a strict temporal separation of ongoing replication in S phase, and the formation of pre-replicative complexes in the preceding G1 phase, which "licenses" each origin competent for replication. The contribution of the loading factor Cdc6 to the timing of the licensing process remained however elusive due to seemingly contradictory findings concerning stabilization, degradation and nuclear export of Cdc6. Using fluorescently tagged Cdc6 (Cdc6-YFP) expressed in living cycling cells, we demonstrate here that Cdc6-YFP is stable and chromatin-associated during mitosis and G1 phase. It undergoes rapid proteasomal degradation during S phase initiation followed by active export to the cytosol during S and G2 phases. Biochemical fractionation abolishes this nuclear exclusion, causing aberrant chromatin association of Cdc6-YFP and, likely, endogenous Cdc6, too. In addition, we demonstrate association of Cdc6 with centrosomes in late G2 and during mitosis. These results show that multiple Cdc6-regulatory mechanisms coexist but are tightly controlled in a cell cycle-specific manner.
authors: a Institute of Clinical Chemistry and Laboratory Diagnostics; University Düsseldorf; Medical Faculty , Düsseldorf , Germany.
authors: Faiza M
authors: FM
authors: Kalfalah
authors: Elke
authors: E
authors: Berg
authors: Morten O
authors: MO
authors: Christensen
authors: René M
authors: RM
authors: Linka
authors: Wilhelm G
authors: WG
authors: Dirks
authors: Fritz
authors: F
authors: Boege
authors: Christian
authors: C
authors: Mielke
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D018385:Centrosome / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology*; D005434:Flow Cytometry; D042822:Genomic Instability / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008938:Mitosis / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C103706:CDC6 protein, human; D018797:Cell Cycle Proteins; D002843:Chromatin; C485182:Cyan Fluorescent Protein; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D018809:Proliferating Cell Nuclear Antigen; C054562:yellow fluorescent protein, Bacteria; D049452:Green Fluorescent Proteins
keywords: APC, anaphase promoting complex; DNA replication; FRAP, fluorescence recovery after photobleaching; MCM, minichromosome maintenance complex; ORC, origin recognition complex; PCNA, proliferating cell nuclear antigen; STR, small tandem repeat; cell cycle control; centrosome; licensing; nuclear export; ori, origin of replication; preRC, pre-replicative complex