Cell Cycle E2F Restriction Point

Transcription factors are amongst the proteins that help regulate the cell cycle. The E2F family of transcription factors are required for the cell to progress to the S-phase. The family is involved in the transcription of proteins that are required for the DNA synthesis stage of the cell cycle. The activation of S phase genes is an important checkpoint for the cell because it commits the cell to going through the cell cycle and is the checkpoint referred to as the “point of no return” for this reason. The E2F transcription factor is typically inactivated and bound to the pRB. However, when the cell is going through the cell cycle and is ready to enter the S-phase, Cyclin D promotes the kinases CDK4 and CDK6 to phosphorylate pRB. This causes pRB to no longer bind to E2F and E2F is then capable of functioning. After being released, E2F can transcribe the necessary proteins for S-phase. As E2F is important for the initiation of S-phase, it is also important in the inhibition of the cell cycle. Should an event occur where the cell needs to stop the cell cycle, such as the DNA being damaged, the cell will not commit to the cell cycle. At that stage, allowing E2F transcription would allow the DNA damage to be replicated and passed down. Therefore, the E2F family needs to remain inactive while the cell either fixes the damage or starts cell death. E2F is needed to progress through the cell cycle, but it is closely regulated so that the cell does not start the cell cycle process without the necessary requirements.