The tumour suppressor protein p53 is a key element of intracellular anticancer protection. It mediates cell cycle arrest or apoptosis in response to DNA damage or to starvation for pyrimidine nukleotides. It is up-regulated in response to these stress signals and stimulated to activate transcription of specific genes, resulting in expression of p21waf1 and other proteins involved in G1 or G2/M arrest, or proteins that trigger apoptosis, such as Bcl-2. The structure of p53 comprises N-terminal transactivation domain, central DNA-binding domain, oligomerisation domain, and C-terminal regulatory domain. There are various phosphorylation sites on p53, of which the phosphorylation at Ser15 is important for p53 activation and stabilization.The antibody BP53-12 recognizes defined epitope (aa 16-25) on human p53, a 50 kDa tumour suppressor found in increased amounts in a wide variety of transformed cells; it is frequently mutated or inactivated in many types of cancer.