Increase of spontaneous intrachromosomal homologous recombination in mammalian cells expressing a mutant p53 protein.

Homologous recombination plays an essential role in processes involved in genome stability/instability, such as molecular evolution, gene diversification, meiotic chromosome segregation, DNA repair and chromosomal rearrangements. p53 devoid cells exhibit predisposition to neoplasia, defects in G1 checkpoint and high genetic instability but a normal rate of point mutations. We investigated the effect of a p53 mutation, on spontaneous homologous recombination between intrachromosomal direct repeat sequences, in mouse L cells. In these cells, wild type for the p53 gene, we have overexpressed the mutant p53(175(Arg>His)) protein leading to a p53 mutant phenotype, as verified by the absence of a G1 arrest after gamma-irradiation. We show that the rate of spontaneous recombination is increased from five- to 20-fold in the mutant p53 lines. Moreover, this increase is observed in gene conversion as well as in deletion events. Our results provide new insights into the molecular mechanisms of genetic instability due to a defect of p53.