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Nucleic Acids Res. 2008 Jun;36(10):3297-310. doi: 10.1093/nar/gkn184. Epub 2008 Apr 24.

Human DNA ligases I and III, but not ligase IV, are required for microhomology-mediated end joining of DNA double-strand breaks.

Author information

1
Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA. liang@biology.rutgers.edu

Abstract

DNA nonhomologous end-joining (NHEJ) and homologous recombination are two distinct pathways of DNA double-strand break repair in mammalian cells. Biochemical and genetic studies showed that DNA ends can also be joined via microhomology-mediated end joining (MHEJ), especially when proteins responsible for NHEJ, such as Ku, are reduced or absent. While it has been known that Ku-dependent NHEJ requires DNA ligase IV, it is unclear which DNA ligase(s) is required for Ku-independent MHEJ. In this study, we used a cell-free assay to determine the roles of DNA ligases I, III and IV in MHEJ and NHEJ. We found that siRNA mediated down-regulation of DNA ligase I or ligase III in human HTD114 cells led to impaired end joining that was mediated by 2-, 3- or 10-bp microhomology. In addition, nuclear extract from human fibroblasts harboring a mutation in DNA ligase I displayed reduced MHEJ activity. Furthermore, treatment of HTD114 nuclear extracts with an antibody against DNA ligase I or III also significantly reduced MHEJ. These data indicate that DNA ligases I and III are required in MHEJ. DNA ligase IV, on the contrary, is not required in MHEJ but facilitates Ku-dependent NHEJ. Therefore, MHEJ and NHEJ require different DNA ligases.

PMID:
18440984
PMCID:
PMC2425475
DOI:
10.1093/nar/gkn184
[Indexed for MEDLINE]
Free PMC Article

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