This family consists of several eukaryotic DNA double-strand break repair and V(D)J recombination protein XRCC4 sequences. In the non-homologous end joining pathway of DNA double-strand break repair, the ligation step is catalysed by a complex of XRCC4 and DNA ligase IV. It is thought that XRCC4 and ligase IV are essential for alignment-based gap filling, as well as for final ligation of the breaks [1].

1: Requirement for XRCC4 and DNA ligase IV in alignment-based gap filling for nonhomologous DNA end joining in vitro. Lee JW, Yannone SM, Chen DJ, Povirk LF; Cancer Res 2003;63:22-24. PMID:12517771