RAP80(Receptor Associated Protein 80) also konwn as UIMC1 is a nuclear protein that plays a critical role in the DNA damage response pathway. RAP80 interacts with Brca1 (breast cancer 1) in a complex to recognize and repair DNA lesions. Research studies indicate that the absence of RAP80 in cells results in increased sensitivity to the topoisomerase II inhibitor etoposide. In the absence of functional RAP80, BRCA1 A complex function is suppressed and cells become more sensitive to DNA damage-induced genome instability. RAP80 binds ubiquitinated lysine 63 of histone H2A and H2AX. RAP80 may also function as a repressor of transcription.