p53 is a crucial tumour suppressor mutated in more than 50% of all human cancers.p53 exerts its function mostly as a transcription factor and is regulated largely at the post-translational level.Pre-malignant cells trigger DNA damage signaling pathways, which, in turn, induce multiple post-translational modifications of p53.The p53 tumor suppressor protein participates in cell cycle arrest and apoptosis chiefly as a sequence-specific transcription factor; it induces transcription of genes, whose products either block cell cycle progression (p21/WAF/Cip) or promote apoptosis (Puma, Bax, Noxa).Upon genotoxic stress, p53 undergoes massive post-translational modifications, including acetylation, phosphorylation, ubiquitylation and methylation.These modifications take place both in the N-and C-termini of the p53 proteinand change its conformation and interactions with other regulatory proteins, ultimately resulting in its stabilization and activation.