The role of the Ran GTPase in nuclear assembly and DNA replication: Characterisation of the effects of Ran mutants

Mike Hughes, Chuanmao Zhang, Johanna M. Avis, Christopher J. Hutchison, Paul R. Clarke

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    The Ran GTPase plays a critical role in nucleocytoplasmic transport and has been implicated in the maintenance of nuclear structure and cell cycle control. Here, we have investigated its role in nuclear assembly and DNA replication using recombinant wild-type and mutant Ran proteins added to a cell-free system of Xenopus egg extracts. RanQ69L, and RanT24N prevent lamina assembly, PCNA accumulation and DNA replication. These effects may be due to the disruption of nucleocytoplasmic transport, since both mutants inhibit nuclear import of a protein carrying a nuclear localisation signal (NLS). RanQ69L, which is deficient in GTPase activity, sequesters importins in stable complexes that are unable to support the docking of NLS-proteins at the nuclear pore complex (NPC). RanT24N, in contrast to wild-type Ran-GDP, interacts only weakly with importin α and nucleoporins, and not at all with the import factor p10, consistent with its poor activity in nuclear import. However, RanT24N does interact stably with importin β, Ran binding protein 1 and RCC1, an exchange factor for Ran. We show that Ran-GDP is essential for proper nuclear assembly and DNA replication, the requirement being primarily before the initiation of DNA replication. Ran-GDP therefore mediates the active transport of necessary factors or otherwise controls the onset of S-phase in this system.
    Original languageEnglish
    Pages (from-to)3017-3026
    Number of pages9
    JournalJournal of Cell Science
    Issue number20
    Publication statusPublished - 1998


    • DNA replication
    • Lamin
    • Nucleocytoplasmic transport
    • Ran
    • Ran-binding protein


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