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Visualization of a Ran-GTP Gradient in Interphase and Mitotic Xenopus Egg Extracts

Science  29 Mar 2002:
Vol. 295, Issue 5564, pp. 2452-2456
DOI: 10.1126/science.1068798

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Abstract

The small guanosine triphosphatase Ran is loaded with guanosine triphosphate (GTP) by the chromatin-bound guanine nucleotide exchange factor RCC1 and releases import cargoes in the nucleus during interphase. In mitosis, Ran-GTP promotes spindle assembly around chromosomes by locally discharging cargoes that regulate microtubule dynamics and organization. We used fluorescence resonance energy transfer–based biosensors to visualize gradients of Ran-GTP and liberated cargoes around chromosomes in mitoticXenopus egg extracts. Both gradients were required to assemble and maintain spindle structure. During interphase, Ran-GTP was highly enriched in the nucleoplasm, and a steep concentration difference between nuclear and cytoplasmic Ran-GTP was established, providing evidence for a Ran-GTP gradient surrounding chromosomes throughout the cell cycle.

  • * To whom correspondence should be addressed. E-mail: heald{at}socrates.berkeley.edu (R.H.); kweis{at}uclink4.berkeley.edu(K.W.)

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