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Nature Cell Biology 4, E177–E184 (1 July 2002) | doi:10.1038/ncb0702-e177

The Ran GTPase as a marker of chromosome position in spindle formation and nuclear envelope assembly

Martin Hetzer , Oliver J. Gruss & Iain W. Mattaj

The small GTPase Ran is a key regulator of nucleocytoplasmic transport during interphase. The asymmetric distribution of the GTP-bound form of Ran across the nuclear envelope — that is, large quantities in the nucleus compared with small quantities in the cytoplasm — determines the directionality of many nuclear transport processes. Recent findings that Ran also functions in spindle formation and nuclear envelope assembly during mitosis suggest that Ran has a general role in chromatin-centred processes. Ran functions in these events as a signal for chromosome position.