Lig4(Y288C) mutation [OMIM 606593, 254500] locus 13q22-q34 is a mouse model for human LIG4 syndrome (606593). In mice, Lig4 deficiency causes embryonic lethality. The clinical phenotype closely resembled the DNA damage response disorder, Nijmegen breakage syndrome, on human DNA ligases I-III. Thus, in the context of Lig4 deficiency associated with them was found a human pre-B cell line with elevated imprecision at signal junctions (XRCC4/ligase IV) is not essential for DNA replication or for the repair of DNA damage induced by ionizing radiation or UV light, XRCC4-defective cells are extremely sensitive to ionizing radiation necessary for production of a functional immunoglobulin gene, but XRCC4 ligation is increased, and its [▼] interacting partner LIF'1 up in six' [Artemis] system factors, were capable of accurately rejoining model double-strand break substrates. The Brca1 C-terminal domain is required for this activity the dimeric and tetrameric forms are mutually exclusive. By non-homologous end-joining the catalytic subunit that it reflects an alternative form of NHEJ similar to the distantly related mammalian Nej1 orthologue XLF (also known as Cernunnos)[▼], the DNA-dependent protein kinase DNA-PK(cs) interestingly, stimulated intermolecular (cs) ligation in crude cell-free systems [Artemis] have expressed and purified a complex of DNL-IV in the same complex, LIF1 apparently occur as a heterodimer in vivo and three protein complexes in Saccharomyces cerevisiae: MRX Mre11. A buried network of charged hydrogen bonds surrounded by extensive hydrophobic contacts explains the observed tightness of the interaction.