XLF (also called Cernunnos) is Xrcc4-like-factor, and interacts with the XRCC4-DNA ligase IV complex to promote DNA non-homologous end-joining. It directly interacts with the XRCC4-Ligase IV complex and siRNA-mediated down-regulation of XLF in human cell lines leads to radio-sensitivity and impaired DNA non-homologous end-joining [1]. This family contains Nej1 (non-homologous end-joining factor) [2], and Lif1, ligase-interacting factor [3]. XLF forms one of the components of the NHEJ machinery for DNA non-homologous end-joining [4].

1: XLF interacts with the XRCC4-DNA ligase IV complex to promote DNA nonhomologous end-joining. Ahnesorg P, Smith P, Jackson SP; Cell. 2006;124:301-313. PMID:16439205

2: Cernunnos interacts with the XRCC4 x DNA-ligase IV complex and is homologous to the yeast nonhomologous end-joining factor Nej1. Callebaut I, Malivert L, Fischer A, Mornon JP, Revy P, de Villartay JP; J Biol Chem. 2006;281:13857-13860. PMID:16571728

3: Structure of an Xrcc4-DNA ligase IV yeast ortholog complex reveals a novel BRCT interaction mode. Dore AS, Furnham N, Davies OR, Sibanda BL, Chirgadze DY, Jackson SP, Pellegrini L, Blundell TL; DNA Repair (Amst). 2005; [Epub ahead of print] PMID:16388993

4: XLF-Cernunnos promotes DNA ligase IV-XRCC4 re-adenylation following ligation. Riballo E, Woodbine L, Stiff T, Walker SA, Goodarzi AA, Jeggo PA; Nucleic Acids Res. 2009;37:482-492. PMID:19056826

5: Crystal structure of human XLF/Cernunnos reveals unexpected differences from XRCC4 with implications for NHEJ. Li Y, Chirgadze DY, Bolanos-Garcia VM, Sibanda BL, Davies OR, Ahnesorg P, Jackson SP, Blundell TL; EMBO J. 2008;27:290-300. PMID:18046455