Role of Importin-β in Coupling Ran to Downstream Targets in Microtubule Assembly

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Science  26 Jan 2001:
Vol. 291, Issue 5504, pp. 653-656
DOI: 10.1126/science.1057661

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The guanosine triphosphatase Ran stimulates assembly of microtubule asters and spindles in mitoticXenopus egg extracts. A carboxyl-terminal region of the nuclear-mitotic apparatus protein (NuMA), a nuclear protein required for organizing mitotic spindle poles, mimics Ran's ability to induce asters. This NuMA fragment also specifically interacted with the nuclear transport factor, importin-β. We show that importin-β is an inhibitor of microtubule aster assembly in Xenopus egg extracts and that Ran regulates the interaction between importin-β and NuMA. Importin-β therefore links NuMA to regulation by Ran. This suggests that similar mechanisms regulate nuclear import during interphase and spindle assembly during mitosis.

  • * These authors contributed equally to this work.

  • To whom correspondence should be addressed. E-mail: a.merdes{at}, zheng{at}

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