Centrosomal and cytoplasmic Cdc2/cyclin B1 activation precedes nuclear mitotic events

Exp Cell Res. 2000 May 25;257(1):11-21. doi: 10.1006/excr.2000.4872.


The activation of cdc2/cyclin B is the trigger for entry into mitosis. The mechanism of cdc2/cyclin B activation is complex, but the final step is the dephosphorylation of the Thr14 and Tyr15 residues on the cdc2 subunit, catalyzed by a member of the Cdc25 family of phosphatases. Cdc2/cyclin B1 accumulates at the centrosome in late G2 phase and has been implicated in the conversion of the centrosome from an interphase to a mitotic microtubule organizing center. Here we demonstrate biochemically that cdc2/cyclin B1 accumulates at the centrosome in late G2 as the inactive, phosphotyrosine 15 form and that the centrosomal cdc2/cyclin B1 can be activated in vitro by recombinant cdc25B. We provide evidence that a portion of the cdc2/cyclin B1 translocated into the nucleus in prophase is the inactive tyrosine-15-phosphorylated form. At this time the centrosomal and cytoplasmic cdc2/cyclin B1 is already active. This provides evidence that the activation of cdc2/cyclin B1 is initiated in the cytoplasm and that full activation of the translocated pool occurs in the nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CDC2 Protein Kinase / metabolism*
  • Cell Nucleus / metabolism
  • Cell Nucleus / ultrastructure
  • Centrosome / metabolism*
  • Centrosome / ultrastructure
  • Cyclin B / metabolism*
  • Cyclin B1
  • Enzyme Activation
  • Humans
  • Mitosis*
  • Signal Transduction
  • T-Lymphocytes / cytology*
  • T-Lymphocytes / metabolism*
  • Tumor Cells, Cultured


  • CCNB1 protein, human
  • Cyclin B
  • Cyclin B1
  • CDC2 Protein Kinase