The p53 functional circuit.

The p53 gene is a tumor suppressor gene that plays a critical role in safeguarding the integrity of the genome. p53 is mutated or part of its regulatory circuit is functionally inactivated in almost all cancers, which highlights its importance in preventing tumorigenesis. The p53 protein is a sequence-specific DNAbinding transcription factor that is kept at a low level in cells under normal circumstances. Various stress signals, such as DNA damage, can stabilize and activate p53. Upon activation, p53 binds to the enhancer/promoter elements of downstream target genes and regulates their transcription, through which it initiates cellular programs that account for most of its tumor-suppressor functions.