Rap80 (Receptor Associated Protein 80) interacts with BRCA1, a ubiquitin E3-ligase which functions in conjugation with the BARD1 deubiquitinating enzyme. BRCA1 is recruited to DNA damage sites by poly-ubiquitin chains through Rap80 which contains 2 tandem ubiquitin-interacting motifs (UIMs). Rap80 constitutes a protein complex with ABRA1 which interacts with the BRCT domain of BRCA1. Upon DNA damage the Rap80-ABRA1 complex targets the BRCA1-BARD1 complex to K6- and K63-linked poly-Ub chains at these foci. The UIM domains of Rap80 have been shown to have preferential binding to K-6 and K63-linked Ub chains and binds to K48-chain with a much lower efficiency. It is not known if Rap80 UIMs interact with Ub chains linked via K11, K27 or K33. Rap80 has a low affinity for mono-, di- and tri-Ub but binds efficiently to tetra (or greater) ubiquitin chains. This protein can be used for the isolation and identification of ubiquitinated proteins that are non-K48-linked. This protein is His-tagged which allows for metal chelate affinity purification and also allows for convenient immuno-detection of conjugates using His6-specific antibodies.