Hot-spot p53 mutants interact specifically with two cellular proteins during progression of the cell cycle.

Inactivation of both alleles of the p53 gene is commonly found in human cancers. In contrast to mutations of the retinoblastoma gene, certain altered forms of p53 gain growth-promoting functions. To explore the mechanisms underlying this gain of function, we have identified two nuclear proteins, with molecular masses of 42 and 38 kDa, respectively, that are specifically associated with p53 mutated within the simian virus 40 T-antigen-binding domain, "hot spots" found in many human tumors. These mutants transactivate the multiple-drug resistance gene promoter and cause cells to grow to higher density. Both the mutated p53 complex with p42 and p38 increase when cells enter S phase of the cell cycle but decrease in G1 and M phases, suggesting that they may have a role in promoting cell growth.