title: Intrinsic nuclear import activity of geminin is essential to prevent re-initiation of DNA replication in Xenopus eggs.
abstract: Prior to S phase, eukaryotic chromosomes are licensed for initiation of DNA replication, and re-licensing is prohibited after S phase has started until late mitosis, thus ensuring that genomic DNA is duplicated precisely once in each cell cycle. Here, we report that over-expression of Cdt1, an essential licensing protein, induced re-replication in Xenopus egg extracts. Geminin, a metazoan-specific inhibitor of Cdt1, was critical for preventing re-replication induced by Cdt1. Re-replication induced by the addition of recombinant Cdt1 and/or by the depletion of geminin from extracts was enhanced by a proteasome inhibitor, which suppressed the degradation of Cdt1 in the extracts. Furthermore, a nuclear localization sequence identified in Xenopus geminin had a significant role in the suppression of re-replication induced by Cdt1. These results suggest that nuclear accumulation of geminin plays a dominant role in the licensing system of Xenopus eggs.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Yoshida
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Takisawa
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Kubota
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D064248:Geminin; D006801:Humans; D019913:Nuclear Localization Signals; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D061988:Proteasome Inhibitors; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: C406819:Cdt1 protein, Xenopus; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C577998:GMNN protein, Xenopus; D064248:Geminin; D019913:Nuclear Localization Signals; D061988:Proteasome Inhibitors; D011994:Recombinant Proteins; D029867:Xenopus Proteins