Ran-independent nuclear import of cyclin B1-Cdc2 by importin beta.
Mitosis is triggered in vertebrate cells by the cyclin B1-Cdc2 complex. The activation of this complex at the end of G2 phase is accompanied by its translocation from the cytoplasm to the nucleus. We used digitonin-permeabilized human cells to analyze the mechanism by which cyclin B1-Cdc2 is imported into the nucleus. Cyclin B1-Cdc2 import was not blocked by inhibitors of the importin alpha-dependent import pathway or by dominant negative versions of the GTPase Ran or importin beta. However, the rate of cyclin B1 import was decreased by immunodepletion of importin beta from cytosol. Purified importin beta promoted cyclin B1 import in the absence of cytosol or Ran and in the presence of the dominant negative Ran mutant. We conclude that cyclin B1 import is mediated by an unusual importin beta-dependent mechanism that does not require Ran.
Department of Physiology, University of California, San Francisco, CA 94143, USA.
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CG
Takizawa
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K
Weis
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DO
Morgan
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D019204:GTP-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera; D014162:Transfection; D020931:ran GTP-Binding Protein
C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D028884:Karyopherins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D016203:CDC2 Protein Kinase; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein