title: Cdk1 and Cdk2 activity levels determine the efficiency of replication origin firing in Xenopus.
abstract: In this paper, we describe how, in a model embryonic system, cyclin-dependent kinase (Cdk) activity controls the efficiency of DNA replication by determining the frequency of origin activation. Using independent approaches of protein depletion and selective chemical inhibition of a single Cdk, we find that both Cdk1 and Cdk2 are necessary for efficient DNA replication in Xenopus egg extracts. Eliminating Cdk1, Cdk2 or their associated cyclins changes replication origin spacing, mainly by decreasing frequency of activation of origin clusters. Although there is no absolute requirement for a specific Cdk or cyclin, Cdk2 and cyclin E contribute more to origin cluster efficiency than Cdk1 and cyclin A. Relative Cdk activity required for DNA replication is very low, and even when both Cdk1 and Cdk2 are strongly inhibited, some origins are activated. However, at low levels, Cdk activity is limiting for the pre-replication complex to pre-initiation complex transition, origin activation and replication efficiency. As such, unlike mitosis, initiation of DNA replication responds progressively to changes in Cdk activity at low activity levels.
authors.affiliation: Laboratory of Phosphorylation and Cell Cycle Control, Institut de Génétique Moléculaire de Montpellier, CNRS, UMR5535, Montpellier, France.
authors.forename: Liliana
authors.initials: L
authors.lastname: Krasinska
authors.forename: Emilie
authors.initials: E
authors.lastname: Besnard
authors.forename: Emilie
authors.initials: E
authors.lastname: Cot
authors.forename: Christiane
authors.initials: C
authors.lastname: Dohet
authors.forename: Marcel
authors.initials: M
authors.lastname: Méchali
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Lemaitre
authors.forename: Daniel
authors.initials: D
authors.lastname: Fisher
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002457:Cell Extracts / Q000302:isolation & purification; D002843:Chromatin / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004261:DNA Replication; D009865:Oocytes / Q000737:chemistry; D014981:Xenopus
chemical_list: D002457:Cell Extracts; D002843:Chromatin; D004247:DNA; D016203:CDC2 Protein Kinase; D051357:Cyclin-Dependent Kinase 2