Germline mutations in the breast cancer susceptibility gene BRCA1 predispose women to breast and ovarian cancer. BRCA1 is involved in many cellular processes, DNA repair, transcription, cell cycle, chromatin remodeling, and apoptosis. Although the tumor suppressor activity of BRCA1 seems to be attributed to its involvement in DNA repair system, its mechanism is still unclear. We have established a laser light micro-irradiation system to create various types of DNA damage in living cells including DNA double-strand breaks (DSBs), single-strand breaks (SSBs), and base damage, which has enabled us to detect BRCA1 accumulation at the site of DNA damage in a real-time course. Furthermore, we generated local UV irradiation in cell nuclei by an isopore membrane filter and analyzed the BRCA1 response to UV irradiation by immunocytochemistry. We found that the N and the Cterminus of BRCA1 independently accumulated at DSBs with distinct kinetics. N-terminal BRCA1 accumulated immediately after laser-irradiation at DSBs and dissociated rapidly. In contrast, the C-terminus of BRCA1 accumulated more slowly at DSBs, but remained at the sites. Interestingly, the N and the C-terminus of BRCA1 accumulate at the site of DSBs, dependent on distinct repair factors. Furthermore, we found that BRCA1 accumulates at SSBs via its C-terminus. These demonstrate that different BRCA1 interactions with repair factors influence its multifunction in DNA repair. Furthermore, BRCA1 immediately accumulated at the locally UV-irradiated sites. The accumulation was abrogated by treatment with transcription inhibitors. BRCA1 accumulates to the UV irradiated sites via its N and C-terminus. The BRCA1 accumulation was dependent on the presence of another DNA repair protein, which is involved in transcription coupled repair. These finding suggest that BRCA1 is involved in transcription coupled repair pathway. These precise analyses of BRCA1 DNA repair function will contribute to the development of molecular diagnosis and molecular targeting therapies for personalized medicine.