CCDC98, also known as Abraxas 1, was identified through protein binding studies using the breast and ovarian predisposition protein BRCA1 as the binding target. CCDC98 recruits RAP80, a ubiquitin-binding protein, to BRCA1, allowing the formation of BRCA1 foci in response to DNA damage caused by ionizing radiation. Both CCDC98 and RAP80 are required for DNA damage resistance, G2-M checkpoint control, and DNA repair. Cells depleted of either CCDC98 or RAP80 exhibited increased sensitivity to ionizing radiation, although not as much as in BRCA1-depleted cells, suggesting that CCDC98 and RAP80 control only part of the DNA damage response role of BRCA1. At least two isoforms of CCDC98 are known to exist.