CtIP is predominantly a nuclear protein that complexes with both BRCA1 and the BRCA1-associated RING domain protein (BARD1). At the protein level, CtIP expression varies with cell cycle progression in a pattern identical to that of BRCA1. Thus, the steady-state levels of CtIP polypeptides, which remain low in resting cells and G1 cycling cells, increase dramatically as Dividing cells traverse the G1/S boundary. CtIP can potentially modulate the functions ascribed to BRCA1 in transcriptional regulation, DNA repair, and/or cell cycle checkpoint control. This N-terminal domain carries a coiled-coil region and is essential for homodimerization of the protein. The C-terminal domain is family pfam08573.