Cyclin A-kinase regulation of E2F-1 DNA binding function underlies suppression of an S phase checkpoint.

Commitment of mammalian cells to enter S phase enables the transcription factor E2F-1 to activate certain genes whose products mediate cell cycle advance. In S phase, E2F-1 forms stable complexes with cyclin A-kinase, which in turn eliminates E2F-1DNA binding function. Here, we show that suppression of E2F-1 DNA-binding activity by cyclin A-kinase is linked to orderly S phase progression. Disruption of this linkage resulted in S phase delay/arrest followed by regrowth or apoptosis, depending upon whether the DNA-bound E2F-1 could transactivate. Hence, the unscheduled presence of E2F-1 on specific DNA sequences during S phase can activate a specific S phase checkpoint, thereby linking transcription, DNA replication, and cell cycle control.