Cdk2 kinase is required for entry into mitosis as a positive regulator of Cdc2-cyclin B kinase activity

Cell. 1996 Jan 12;84(1):73-82. doi: 10.1016/s0092-8674(00)80994-0.


In higher eukaryotes, Cdk2 kinase plays an essential role in regulating the G1-S transition. Here, we use cycling Xenopus egg extracts to examine the requirement of Cdk2 kinase on progression into mitosis. Interestingly, when Cdk2 kinase activity is inhibited by the Cdk-specific inhibitor, p21Cip1, a block to mitosis occurs, and inactive Cdc2-cyclin B accumulates. This block occurs in the absence of nuclei and is not due to direct inhibition of Cdc2 by Cip. Importantly, this block to mitosis is reversible by restoring Cdk2-cyclin E kinase activity to a Cip-treated cycling extract. Moreover, immunodepletion of Cdk2 from interphase extracts prevents activation of Cdc2 upon the addition of exogenous cyclin B. Thus, our data show that Cdk2 kinase is a positive regulator of Cdc2-cyclin B complexes and establish a link between Cdk2 kinase and cell cycle progression into mitosis.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • CDC2 Protein Kinase / antagonists & inhibitors
  • CDC2 Protein Kinase / metabolism*
  • CDC2-CDC28 Kinases*
  • Cell Cycle / physiology
  • Cell Extracts
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclin-Dependent Kinases / physiology*
  • Cyclins / metabolism*
  • Cyclins / pharmacology
  • DNA Replication / physiology
  • Enzyme Inhibitors / metabolism
  • Enzyme Inhibitors / pharmacology
  • Mitosis / physiology*
  • Ovum / cytology
  • Ovum / enzymology
  • Protein-Serine-Threonine Kinases / physiology*
  • S Phase / physiology
  • Xenopus
  • Xenopus Proteins


  • Cell Extracts
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Enzyme Inhibitors
  • Xenopus Proteins
  • Protein-Serine-Threonine Kinases
  • CDC2 Protein Kinase
  • CDC2-CDC28 Kinases
  • Cdk2 protein, Xenopus
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases