XCDT1 is required for the assembly of pre-replicative complexes in Xenopus laevis.
In eukaryotic cells, chromosomal DNA replication begins with the formation of pre-replication complexes at replication origins. Formation and maintenance of pre-replication complexes is dependent upon CDC6 (ref. 1), a protein which allows assembly of MCM2-7 proteins, which are putative replicative helicases. The functional assembly of MCM proteins into chromatin corresponds to replication licensing. Removal of these proteins from chromatin in S phase is crucial in origins firing regulation. We have identified a protein that is required for the assembly of pre-replication complexes, in a screen for maternally expressed genes in Xenopus. This factor (XCDT1) is a relative of fission yeast cdt1, a protein proposed to function in DNA replication, and is the first to be identified in vertebrates. Here we show, using Xenopus in vitro systems, that XCDT1 is required for chromosomal DNA replication. XCDT1 associates with pre-replicative chromatin in a manner dependent on ORC protein and is removed from chromatin at the time of initiation of DNA synthesis. Immunodepletion and reconstitution experiments show that XCDT1 is required to load MCM2-7 proteins onto pre-replicative chromatin. These findings indicate that XCDT1 is an essential component of the system that regulates origins firing during S phase.
Maiorano
D
D
Institute of Human Genetics, CNRS, Genome Dynamics and Development, Montpellier, France.
Moreau
J
J
Méchali
M
M
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology; D002843:Chromatin / Q000502:physiology; D003001:Cloning, Molecular; D004261:DNA Replication / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D064148:Minichromosome Maintenance Complex Component 4; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D011485:Protein Binding; D018741:Replication Origin / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000502:physiology; D029867:Xenopus Proteins; D014982:Xenopus laevis
C406819:Cdt1 protein, Xenopus; D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins; C092802:MCM4 protein, S cerevisiae; C099243:MCM4 protein, human; D064148:Minichromosome Maintenance Complex Component 4