MRE11 and breast cancer: The main functional domains of Nbs1 comprise the forkhead-associated (FHA) domain (amino acids 24–100), the breast cancer C-terminal (BRCT) domain (amino acids 105–190), the second BRCT domain (amino acids 215–324), and the Mre11-binding domain (amino acids 601–700, binding sites 665–693), as well as ATM phosphorylation sites [13,14].