The Trp53 gene encodes tumor protein p53, which involves in diverse cellular stresses to regulate target genes that induce cell cycle arrest, apoptosis, senescence, DNA repair, or changes in metabolism. P53 protein is expressed at low level in normal cells and at a high level in a variety of transformed cell lines. Mice with homozygous p53 inactivation are developmentally normal but are susceptible to spontaneous tumors.