A, B and C complex of BRCA1 contributes to BRCA1's role in cell cycle checkpoint regulation and DNA repair. In addition to forming C-terminal associated complexes, BRCA1 contains a coiled-coil domain upstream of BRCT domain, which interacts with a coiled-coil domain at the N-terminus of PALB2. PALB2 associates with BRCA2 thus bridging the interaction of BRCA1 and BRCA2 [117–119]. The N-terminus RING domain, in addition to dimerizing with BARD1 forming an E3 ligase, this region is also reported to interact with a ubiquitin hydrolase BAP1 [120, 121]. Previous studies suggested that the central region of BRCA1 is also reported to interact with multiple proteins either directly or indirectly [115, 116]. In addition, BRCA1 contains a S/TQ cluster that is phosphorylated by ATM/ATR at multiple sites and the phosphorylation is critical for BRCA1's role in cell cycle checkpoints regulation in the DDR . BRCA1 has also been reported to be a substrate of Chk2 at S988 .