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The p53 amino sequence has an acidic N-terminal domain, reminiscent of many transcription factors(NF-Kappa B), which is able in chimeric proteins to substitute for the DNA-binding domain of the GAL4 transcription factor. DNA sequences that bind p53 have been identified; the protein binds as a tetramer.
Genes with p53-binding sequences near their 5'-ends are activated when cellular levels of p53 are increased. But there are other effects. It's capable of binding to TATA binding proteins, and other transcription factors.
To judge by its effects in restraining cell growth, the sequence transcribed under the control of p53 must have products that oppose to proliferation; though proved by transgenic mice experiments, p53 is not essential for this.The activity of p53 itself is under the control of several viral oncogenes, such as SV 40 large T antigen and the papilloma virus E6 protein. These viral proteins bind to p53 and cause it be degraded by intracellular proteases. Also, the products of mdm2 gene, an oncogene amplified very much in sarcomas, interact with and inactivates p53.
But there is more to p53 than that. DNA damage induced p53 transcription and translation. One set of genes activated through p53's activation is concerned with the cellular response to damage; and cells deficient or mutated in p53 show two striking features: 1) They're insensitive to DNA damage and carry on with DNA replication without arresting their progression into the S phase. this obviously leads to a higher rate of mutation. 2) p53 deficiency or mutation strikingly increase the amplification of random segments of the damaged genome. Inevitably, cellular oncogene sequences are among them. Lastly, p53 promote apoptosisafter growth arrest
Mutations in p53 have a remarkable potential of accelerating tumor development: they will make mutations and amplification of oncogenes more likely, and make other tumor supreesor gene become inactivatedm and prevent cell death in overcrowded conditions.