Its recruitment to DNA double strand breaks is facilitated by the damage sensor MRN and is critical for further assembly and employment of other recombination proteins to the site. BRCA1 consists of N-terminal RING domain and C-terminal tandem BRCT domains. The RING domain mediates its interaction with BARD1. Through the BRCT domains, it forms several distinct complexes including BRCA1-Abraxas, BRCA1-BACH1 and BRCA1-CtIP that perform key roles during initiation of recombination. In addition, it functions in other DNA repair pathways such as non-homologous end joining and nucleotide excision repair pathways, and is also part of BASC in genome surveillance. Several studies implicate BRCA1 in Ezutromid telomere maintenance. BRCA1 deficiency results in telomere dysfunction, as evidenced by elevated chromosome fusions and translocations involving telomeres and telomere shortening. Brca12/2 ML264 murine T-cells display a high incidence of telomere instability, while expression of dominant-negative BRCA1 in human cells results in telomere dysfunction. BRCA1 interacts with the telomere binding proteins TRF1 and TRF2 and is localized to telomeres. Its overexpression inhibits telomerase transcription and promotes shortening of telomeres in telomerase-positive breast and prostate cancer cell lines. Interestingly, BRCA1 knockdown increases telomere length in some telomerase-positive cells. An essential role of BRCA1 in telomere length maintenance is further emphasized by recent reports on telomere length measurements in those with familial breast cancer indicating a correlation between telomere shortening in these affecteds and age of breast cancer onset. The biochemical mechanisms by which BRCA1 mediates telomere maintenance are undefined. Although BRCA1 interacts with the recQ-like helicases WRN and BLM to facilitate intrastrand cross-link repair and DSB repair, BRCA1 interaction with BLM in the context of telomere metabolism is unclear. This study explores the role of BLM and BRCA1 in telomere metabolism in ALT cells. Our recent study demonstrated that telomerase-negative tumor cell lines utilize different ALT mechanisms to maintain telomeres.