<prompt> Which of the following is known as the guardian of the genome -p53Mdm2p14ATM  <response>: p53; Guardian of genomep53 is a tumor suppressor gene.p53 gene is located on chromosome 17.p53 acts as molecular policeman that prevents the propagation of genetically damage cell.p53 gene product, i.e. p53 protein is a DNA binding protein in the nucleus, when called into action, it controls the transcription of several other genes.The ma or functional activities of the 53 rotein are cell c cle arrest and initiation of a o v.tosis in res onse to DNA damage.When there is DNA damage due to irradiation, UV light or mutagenic chemicals, there is rapid increase in p53 levels.p53 causes -Cell cycle arrestp-53 induces transcription of p21, a CDK inhibitor.p21 inhibit cyclin D-CDK-4 complex and there is arrest of cell cycle late in G1 phase.This allows time for DNA repair.DNA repairp-53 also helps in DNA repair directly by inducing transcription of GADD 45 growth arrest and DNA damage.GADD 45 encodes a protein that is involved in DNA repair.If DNA damage is repaired successfully, p53 activate MDM-3 and this MDM-3 induce degradation of p-53 Relieve in cell cycle block.If DNA damage cannot be successfully repaired, p53 induces apoptosis by inducing the activation of apoptosis-inducing gene BAX.So p53 prevents replication of cell with defective DNA p53 functions as a critical gatekeeper against the formation of cancer.Mutation in p53 leads to carcinogenesis because of loss of the above protective mechanism.p-53 is the most common target for genetic alteration in human tumors: A little over 50 of human tumors contain mutation in this gene. Note - Amongst oncogene RAS is involved most commonly. 