(The name of) a multifunctional protein involved in transcription and regulation of the cell cycle, including inhibition of abnormal cell proliferation, and thus implicated in tumour suppression (or, under certain circumstances, promotion). Also (more fully "p53 gene"): the gene encoding this protein, found (in humans) on chromosome 17.
1970s. From p- + fifty + three (the molecular mass of the protein being approx. 53,000). Written with numerical symbol for the second element.