1. DNA ligase III and DNA ligase IV carry out genetically distinct forms of end joining in human somatic cells
- Author
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Adam J. Harvey, Sehyun Oh, Eric A. Hendrickson, Pauline Jackson, Yongbao Wang, Thanh Nguyen, and Jacob Zimbric
- Subjects
DNA End-Joining Repair ,Ku80 ,DNA Ligases ,DNA repair ,Xenopus Proteins ,LIG4 ,Biology ,Biochemistry ,Article ,Cell Line ,DNA Ligase ATP ,Humans ,Poly-ADP-Ribose Binding Proteins ,Ku Autoantigen ,Molecular Biology ,chemistry.chemical_classification ,DNA ligase ,fungi ,Gene targeting ,Antigens, Nuclear ,Cell Biology ,HCT116 Cells ,Molecular biology ,DNA-Binding Proteins ,Non-homologous end joining ,enzymes and coenzymes (carbohydrates) ,chemistry ,embryonic structures ,Homologous recombination - Abstract
Ku-dependent C-NHEJ (classic non-homologous end joining) is the primary DNA EJing (end joining) repair pathway in mammals. Recently, an additional EJing repair pathway (A-NHEJ; alternative-NHEJ) has been described. Currently, the mechanism of A-NHEJ is obscure although a dependency on LIGIII (DNA ligase III) is often implicated. To test the requirement for LIGIII in A-NHEJ we constructed a LIGIII conditionally-null human cell line using gene targeting. Nuclear EJing activity appeared unaffected by a deficiency in LIGIII as, surprisingly, so were random gene targeting integration events. In contrast, LIGIII was required for mitochondrial function and this defined the gene’s essential activity. Human Ku:LIGIII and Ku:LIGIV (DNA ligase IV) double knockout cell lines, however, demonstrated that LIGIII is required for the enhanced A-NHEJ activity that is observed in Ku-deficient cells. Most unexpectedly, however, the majority of EJing events remained LIGIV-dependent. In conclusion, although human LIGIII has an essential function in mitochondrial maintenance, it is dispensable for most types of nuclear DSB repair, except for the A-NHEJ events that are normally suppressed by Ku. Moreover, we describe that a robust Ku-independent, LIGIV-dependent repair pathway exists in human somatic cells.
- Published
- 2014