You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following is known as the "guardian of the genome" - and explain in detail?
p53; Guardian of genome

p53 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 arrest


p-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 repair

p-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).