INTERACTION OF P53 WITH THE HUMAN RAD51 PROTEIN

p53 is thought to function in the maintenance of genomic stability by modulating transcription and interacting with cellular proteins to inf luence the cell cycle, DNA repair and apoptosis. p53 mutations occur i n >50% of human cancers, and cells which lack wild type p53 accumulate karyotypic abnormalities such as amplifications, deletions, inversion s and translocations, We propose that p53 hinders these promiscuous re combinational events by interacting with cellular recombination and re pair machinery. We recently reported that p53 can directly bind in viv o to human Rad51 (hRad51) protein and in vitro to its bacterial homolo gue RecA. We used GST-fusion and his-tagged protein systems to further investigate the physical interaction between p53 and hRad51, homologu e of the yeast Rad51 protein that is involved in recombination and DNA double strand repair. The hRad51? binds to wild-type p53 and to a les ser extent, point mutants 135Y, 249S and 273H. This binding is not med iated by a DNA or RNA intermediate, Mapping studies using a panel of p 53 deletion mutants indicate that hRad51 could bind to two regions of p53; one between amino acids 94 and 160 and a second between 264 and 3 15, Addition of anti-p53 antibody PAb421 (epitope 372-381 amino acids) inhibited the interaction with hRad51. In contrast, p53 interacts wit h the region between aa 125 and 220 of hRad51, which is highly conserv ed among Rad51 related proteins from bacteria to human, In Escherichia coil RecA protein, this region is required for homo-oligomerization, suggesting that p53 might disrupt the interaction between RecA and Rad 51 subunits, thus inhibiting biochemical functions of Rad51 like prote ins, These data are consistent with the hypothesis that p53 interactio n with hRAD51 may influence DNA recombination and repair and that addi tional modifications of p53 by mutation and protein binding may affect this interaction.