Role of importin-beta in coupling Ran to downstream targets in microtubule assembly.
The guanosine triphosphatase Ran stimulates assembly of microtubule asters and spindles in mitotic Xenopus 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-beta. We show that importin-beta is an inhibitor of microtubule aster assembly in Xenopus egg extracts and that Ran regulates the interaction between importin-beta and NuMA. Importin-beta therefore links NuMA to regulation by Ran. This suggests that similar mechanisms regulate nuclear import during interphase and spindle assembly during mitosis.
Department of Embryology, Howard Hughes Medical Institute, Carnegie Institution of Washington, Baltimore, MD 21210, USA.
C
C
Wiese
A
A
Wilde
M S
MS
Moore
S A
SA
Adam
A
A
Merdes
Y
Y
Zheng
D000818:Animals; D002457:Cell Extracts; D002467:Cell Nucleus / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007399:Interphase; D028884:Karyopherins; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D008938:Mitosis; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism* / Q000494:pharmacology; D010063:Ovum; D017239:Paclitaxel / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism*; D014981:Xenopus; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D002457:Cell Extracts; D028884:Karyopherins; C489079:NUMA1 protein, Xenopus; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein; D017239:Paclitaxel