Expression of the tumor suppressor gene p53 is elevated in response to DNA damage by suppressing degradation of p53 protein by the proteasome. What is the role of p53 in response to DNA damage?
1) Activates repair mechanisms to fix DNA damage
2) Initiates cell cycle arrest to allow time for DNA repair
3) Induces apoptosis to eliminate cells with irreparable DNA damage
4) All of the above