Stimulation of Microtubule Aster Formation and Spindle Assembly by the Small GTPase Ran

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Science  21 May 1999:
Vol. 284, Issue 5418, pp. 1359-1362
DOI: 10.1126/science.284.5418.1359

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Ran, a small guanosine triphosphatase, is suggested to have additional functions beyond its well-characterized role in nuclear trafficking. Guanosine triphosphate–bound Ran, but not guanosine diphosphate–bound Ran, stimulated polymerization of astral microtubules from centrosomes assembled on Xenopus sperm. Moreover, a Ran allele with a mutation in the effector domain (RanL43E) induced the formation of microtubule asters and spindle assembly, in the absence of sperm nuclei, in a γTuRC (γ-tubulin ring complex)– and XMAP215 (Xenopusmicrotubule associated protein)–dependent manner. Therefore, Ran could be a key signaling molecule regulating microtubule polymerization during mitosis.

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