EXO1 and Bloom syndrome: The DSB site is bounded by several factors such as the MRN complex, EXO1 (exonuclease 1), DNA2-BLM (Bloom syndrome), BRCA1 and CTIP (CtBP-interacting protein) that contribute to DNA resection and formation of a 3′ single-strand DNA (58–60), which is then coated by proteins of replication A (RPA).