Source:http://linkedlifedata.com/resource/umls/id/C1515680
NCI: p53 is a transcription factor who's activity is regulated by phosphorylation. The function is p53 is to keep the cell from progressing through the cell cycle if there is damage to DNA present. It may do this in multiple ways from holding the cell at a checkpoint until repairs can be made to causing the cell to enter apoptosis if the damage cannot be repaired. The critical role of p53 is evidenced by the fact that it is mutated in a very large fraction of tumors from nearly all sources.