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.
Wiese
C
C
Department of Embryology, Howard Hughes Medical Institute, Carnegie Institution of Washington, Baltimore, MD 21210, USA.
Wilde
A
A
Moore
M S
MS
Adam
S A
SA
Merdes
A
A
Zheng
Y
Y
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