title: An early S phase checkpoint is regulated by the E2F1 transcription factor.
abstract: 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.
authors.affiliation: Deptartment of Orthopaedic Surgery, Thomas Jefferson University, Room 501 Curtis Building, Philadelphia, Pennsylvania, 19107, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Stubbs
authors.forename: G D
authors.initials: GD
authors.lastname: Strachan
authors.forename: D J
authors.initials: DJ
authors.lastname: Hall
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D051379:Mice; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase / Q000502:physiology*; D013936:Thymidine / Q000378:metabolism; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000502:physiology*
chemical_list: C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D004247:DNA; D013936:Thymidine