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Cell 2001 Jan 12;1041:83-93. doi: 10.1016/s0092-8674(01)00193-3.
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Ran induces spindle assembly by reversing the inhibitory effect of importin alpha on TPX2 activity.

Gruss OJ , Carazo-Salas RE , Schatz CA , Guarguaglini G , Kast J , Wilm M , Le Bot N , Vernos I , Karsenti E , Mattaj IW .

The small GTPase Ran, bound to GTP, is required for the induction of spindle formation by chromosomes in M phase. High concentrations of Ran.GTP are proposed to surround M phase chromatin. We show that the action of Ran.GTP in spindle formation requires TPX2, a microtubule-associated protein previously known to target a motor protein, Xklp2, to microtubules. TPX2 is normally inactivated by binding to the nuclear import factor, importin alpha, and is displaced from importin alpha by the action of Ran.GTP. TPX2 is required for Ran.GTP and chromatin-induced microtubule assembly in M phase extracts and mediates spontaneous microtubule assembly when present in excess over free importin alpha. Thus, components of the nuclear transport machinery serve to regulate spindle formation in M phase.

PubMed ID: 11163242
Article link: Cell

Species referenced: Xenopus laevis
Genes referenced: kif15 ran tpx2

References :
Dasso, Running on Ran: nuclear transport and the mitotic spindle. 2001, Pubmed