Answer :
The p53 protein level is modest in normal cells.
The rise of p53 proteins, which have three key functions: growth arrest, DNA repair, and apoptosis, may be triggered by DNA damage and other stress signals (cell death).The growth arrest halts the cell cycle and prevents the reproduction of damaged DNA.
When DNA damage occurs before the cell cycle enters S phase, p53 arrests the cell cycle in G1 by transcriptionally generating the cyclin-dependent kinase inhibitor cdkn1a, commonly known as p21.