BRCA1 - Function and Mechanism

Function and Mechanism

BRCA1 repairs double-strand breaks in DNA. The strands of the DNA double helix are continuously breaking from damage. Sometimes one strand is broken, and sometimes both strands are broken simultaneously. DNA cross linking agents are an important source of chromosome/DNA damage. Double strand breaks occur as intermediates after the cross links are removed. BRCA1 is part of a protein complex that repairs DNA when both strands are broken. When both strands are broken, it is difficult for the repair mechanism to "know" how to replace the correct DNA sequence, and there are multiple ways to attempt the repair. The double-stranded repair mechanism that BRCA1 participates in is homologous recombination, in which the repair proteins utilize homologous intact sequence from a sister chromatid, from a homologous chromosome, or from the same chromosome (depending on cell cycle phase) as a template. This DNA repair takes place with the DNA in the cell nucleus, wrapped around the histone. Several proteins, including BRCA1, arrive at the histone-DNA complex for this repair. Regulatory aspect to BRCA1 nuclear ⁄ non-nuclear distribution was first shown by Dr Rao laboratory in 1997

In the nucleus of many types of normal cells, the BRCA1 protein interacts with RAD51 during repair of DNA double-strand breaks. These breaks can be caused by natural radiation or other exposures, but also occur when chromosomes exchange genetic material (homologous recombination, e.g., "crossing over" during meiosis). The BRCA2 protein, which has a function similar to that of BRCA1, also interacts with the RAD51 protein. By influencing DNA damage repair, these three proteins play a role in maintaining the stability of the human genome.

BRCA1 directly binds to DNA, with higher affinity for branched DNA structures. This ability to bind to DNA contributes to its ability to inhibit the nuclease activity of the MRN complex as well as the nuclease activity of Mre11 alone. This may explain a role for BRCA1 to promote lower fidelity DNA repair by non-homologous end joining (NHEJ). BRCA1 also colocalizes with γ-H2AX (histone H2AX phosphorylated on serine-139) in DNA double-strand break repair foci, indicating it may play a role in recruiting repair factors.

Formaldehyde and acetaldehyde are common environmental sources of DNA cross links that often require repairs mediated by BRCA1 containing pathways.