Evidence that the G1-S and G2-M transitions are controlled by different cdc2 proteins in higher eukaryotes

Cell. 1991 Aug 23;66(4):731-42. doi: 10.1016/0092-8674(91)90117-h.


Xenopus eggs contain two distinct cdc2 homologs of 34 and 32 kd. We show that the 32 kd cdc2 protein, like the 34 kd protein, is a kinase. However, unlike the 34 kd homolog, the 32 kd cdc2 kinase activity does not decrease dramatically at the end of mitosis. The 32 kd protein does not associate with mitotic cyclins B1 and B2 but does associate with cyclin A and a novel doublet of proteins of 54 kd that may regulate its activity. We also show that depletion of the 32 kd cdc2 homolog from a Xenopus extract blocks DNA replication, but does not inhibit entry into mitosis. By contrast, depletion of the 34 kd cdc2 homolog or absence of mitotic cyclins from an extract does not inhibit replication, but does block entry into mitosis. Our results indicate that in higher eukaryotes, DNA replication (G1-S) and mitosis (G2-M) may be controlled by distinctly different cdc2 proteins.

Publication types

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

MeSH terms

  • Animals
  • CDC2 Protein Kinase / physiology*
  • Cell Cycle Proteins
  • Cell Cycle*
  • Cyclins / metabolism
  • DNA Replication
  • Histones / metabolism
  • Macromolecular Substances
  • Mitosis
  • Periodicity
  • Phosphoproteins / physiology*
  • Protamine Kinase / metabolism
  • Protein Binding
  • Protein Kinases / physiology*
  • Xenopus Proteins*
  • Xenopus laevis


  • Cell Cycle Proteins
  • Cyclins
  • Histones
  • Macromolecular Substances
  • Phosphoproteins
  • Xenopus Proteins
  • Protein Kinases
  • CDK1 protein, Xenopus
  • Protamine Kinase
  • CDC2 Protein Kinase