The core engines that drive the progression through the eukaryotic cell cycle are complexes of cyclins and cyclin dependent kinases. Cdk4-Cyclin D complex is implicated in committing a cell to the G1/S phase transition, Cdk2-Cyclin E in the initiation of S phase and Cdk2-Cyclin A in its completion as well as in S phase exit. CDKN1A that is activated by various kinds of damages to the cell, interact physically with the latter two aforementioned complexes, and inhibit the cell cycle progression. The E2F1-3 protein family members are the major transcription factors (TFs) that regulates the transcription of genes involved in the cell progression from G1 to the S phase.
