p53, also known as tumor protein 53 (TP53), is a transcription factor that regulates the cell cycle and hence functions as a tumor suppressor. It is very important for cells in multicellular organisms to suppress cancer. p53 has been described as "the guardian of the genome" or the "master watchman", referring to its role in conserving stability by preventing genome mutation.
- It can activate DNA repair proteins when DNA has sustained damage.
- It can also hold the cell cycle at the G1/S regulation point on DNA damage recognition.
- It can initiate apoptosis, the programmed cell death, if the DNA damage proves to be irreparable.