A significant fraction of familial breast cancer cases is caused by mutations in the BRCA2 gene. A number of different models for the function of the Brca2 protein have been developed. Recent genetic studies in mice combined with molecular studies of BRCA2 provided compelling evidence for a role in DNA repair. DNA repair is a pivotal cellular process ensuring the integrity of the genome by processing DNA damage and restoring the original DNA sequence. Absence of or failure to accurately repair DNA leads to cell death or mutations. DNA repair defects in humans are known to predispose to cancer, as shown in a variety of cancer susceptibility syndromes that affect a variety of different tissues, including the skin and the colon (xeroderma pigmentosum, HNPCC, ataxia telangiectasia, and BloomÆs and CockayneÆs syndrome). DNA damage arises as a consequence of the inherent instability of the DNA, as a side product of normal cellular processes, and by exposure to environmental agents, many of which are known to cause cancer. The specificity of BRCA2 in causing breast (and ovarian) tumors may be a consequence of tissue-specific differences in the type and extent of the DNA damage that arises in these tissues.

The previous studies have suggested a role in DNA repair for Brca2 protein and that its interaction with the DNA repair protein Rad51 is of biological significance. The role of Rad51 protein in DNA repair is beginning to be understood at the molecular level. It is involved in a complex DNA repair pathway that restores DNA double stranded breaks and other types of DNA damage in a highly accurate way. DNA double stranded breaks are one of the most devastating DNA lesions and can be induced by ionizing radiation like x-rays.

We propose to apply our knowledge and expertise of the Rad51p-dependent DNA repair pathway to elucidate a possible direct molecular role of Brca2 protein in DNA repair. Our hypothesis is that Brca2 protein is a critical accessory protein of the Rad51p-mediated DNA repair. The proposed research includes the purification of Brca2 protein, which will constitute a significant achievement that has not been reported before. Moreover, we will examine Brca2 protein for molecular activities that may be significant in DNA repair. To date, no molecular activity of the Brca2 protein, other than binding to Rad51 protein, has been identified. These studies are intended to elevate the understanding of Brca2 protein to the next level, which is its molecular function.

The biochemical analysis of purified Brca2p is critical to elucidate its molecular function. The molecular function of Brca2 protein is not known at present and our proposal aims at contributing to close the void that exists presently in the purification and biochemical analysis of this protein. Knowledge of the molecular function will help with devising new therapeutic approaches for BRCA2-related tumors based on the molecular role of Brca2p. Moreover, understanding the molecular function of Brca2 protein will help us to understand why mutations in this protein specifically cause breast (and ovarian) cancer, which will impact breast cancer biology beyond the cases caused by mutations in BRCA2.