Cyclin/Cdk-dependent initiation of DNA replication in a human cell-free system

Cell. 1997 Jan 10;88(1):109-19. doi: 10.1016/s0092-8674(00)81863-2.


We describe a cell-free system from HeLa cells that initiates DNA replication under cell cycle control. G1 but not G2 phase nuclei initiate replication when coincubated with S phase nuclei in cytosolic extracts from S phase but not from G1 or G2 phase HeLa cells. S phase nuclei or an S phase nuclear extract are required for the initiation of semiconservative DNA replication in G1 nuclei but not for elongation in S phase nuclei. S phase nuclear extract could be replaced by recombinant human cyclins A and E complexed to Cdk2 but not by Cdk2 alone or by human cyclin B1 complexed to Cdc2. In S phase cytosol, cyclins A/Cdk2 and E/Cdk2 triggered initiation synergistically.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CDC2-CDC28 Kinases*
  • Cell Extracts
  • Cell Nucleus / metabolism
  • Cell-Free System
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases / physiology*
  • Cyclins / physiology*
  • DNA Replication / physiology*
  • G1 Phase / physiology*
  • G2 Phase / physiology
  • HeLa Cells
  • Humans
  • Protein-Serine-Threonine Kinases / physiology*
  • S Phase / physiology*


  • Cell Extracts
  • Cyclins
  • Protein-Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases