An early S phase checkpoint is regulated by the E2F1 transcription factor

Biochem Biophys Res Commun. 1999 Apr 29;258(1):77-80. doi: 10.1006/bbrc.1999.0603.


The E2F1 transcription factor regulates transit of cells through the S phase checkpoint, dependent on its association with cyclin A/cdk2. Expression in cells of a mutant E2F1 lacking the cyclin A/cdk2 binding domain leads to partial arrest of cells at the S phase checkpoint. When subconfluent growing cells expressing this mutant E2F1 are analyzed in detail, it is shown here that they display a significantly reduced incorporation of 3H-thymidine into the DNA of each S phase cell, compared to control cells or to cells overexpressing full-length E2F1. Further, when cells are blocked at the G1/S phase border and released, there is a clear reduction in the amount of 3H-thymidine incorporated into the DNA of S phase cells by 1.5 hours post release. Considering a normal 6 hour S phase duration, the results show that the S phase checkpoint mediated by E2F1 is not a late S phase event but an early one.

Publication types

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

MeSH terms

  • 3T3 Cells
  • Animals
  • Carrier Proteins*
  • Cell Cycle Proteins*
  • DNA / metabolism
  • DNA-Binding Proteins*
  • E2F Transcription Factors
  • E2F1 Transcription Factor
  • Mice
  • Retinoblastoma-Binding Protein 1
  • S Phase / physiology*
  • Thymidine / metabolism
  • Transcription Factor DP1
  • Transcription Factors / physiology*


  • Arid4a protein, mouse
  • Carrier Proteins
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • E2F Transcription Factors
  • E2F1 Transcription Factor
  • E2f1 protein, mouse
  • Retinoblastoma-Binding Protein 1
  • Transcription Factor DP1
  • Transcription Factors
  • DNA
  • Thymidine