XRCC4 (X-ray repair complementing defective repair in Chinese hamster cells 4) is mainly involved in the XRCC4-dependent DNA double-strand repair pathway. Mono-ubiquitinated XRCC4 binds to the ligase for the formation of DNA ligase IV-XRCC4 complex. Generally, ligase is unstable in nature, but in the presence of mono-ubiquitinated XRCC4, it becomes stable during ligation. The complex directly acts on the duplex DNA end part and bridging between the duplex DNA molecules and complementary but non-ligatable ends. Finally, through protein-protein interactions, DNA ligase IV-XRCC4 complex facilitates the intermolecular ligation in the presence of DNA-dependent protein kinase (DNA-PK).
