K63-linked polyubiquitin chains bind to DNA to facilitate DNA damage repair

Polyubiquitylation is canonically viewed as a posttranslational modification that governs protein stability or protein-protein interactions, in which distinct polyubiquitin linkages ultimately determine the fate of modified protein(s). We explored whether polyubiquitin chains have any nonprotein-related function. Using in vitro pull-down assays with synthetic materials, we found that polyubiquitin chains with the Lys(63) (K63) linkage bound to DNA through a motif we called the DNA-interacting patch ( DIP), which is composed of the adjacent residues Thr(9), Lys(11), and Glu(34). Upon DNA damage, the binding of K63-linked polyubiquitin chains to DNA enhanced the recruitment of repair factors through their interaction with an Ile(44) patch in ubiquitin to facilitate DNA repair. Furthermore, experimental or cancer patient-derived mutations within the DIP impaired the DNA binding capacity of ubiquitin and subsequently attenuated K63-linked polyubiquitin chain accumulation at sites of DNA damage, thereby resulting in defective DNA repair and increased cellular sensitivity to DNA-damaging agents. Our results therefore highlight a critical physiological role for K63-linked polyubiquitin chains in binding to DNA to facilitate DNA damage repair.