title: Ligase I and ligase III mediate the DNA double-strand break ligation in alternative end-joining.
abstract: In eukaryotes, DNA double-strand breaks (DSBs), one of the most harmful types of DNA damage, are repaired by homologous repair (HR) and nonhomologous end-joining (NHEJ). Surprisingly, in cells deficient for core classic NHEJ factors such as DNA ligase IV (Lig4), substantial end-joining activities have been observed in various situations, suggesting the existence of alternative end-joining (A-EJ) activities. Several putative A-EJ factors have been proposed, although results are mostly controversial. By using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system, we generated mouse CH12F3 cell lines in which, in addition to Lig4, either Lig1 or nuclear Lig3, representing the cells containing a single DNA ligase (Lig3 or Lig1, respectively) in their nucleus, was completely ablated. Surprisingly, we found that both Lig1- and Lig3-containing complexes could efficiently catalyze A-EJ for class switching recombination (CSR) in the IgH locus and chromosomal deletions between DSBs generated by CRISPR/Cas9 in cis-chromosomes. However, only deletion of nuclear Lig3, but not Lig1, could significantly reduce the interchromosomal translocations in Lig4(-/-) cells, suggesting the unique role of Lig3 in catalyzing chromosome translocation. Additional sequence analysis of chromosome translocation junction microhomology revealed the specificity of different ligase-containing complexes. The data suggested the existence of multiple DNA ligase-containing complexes in A-EJ.
authors.affiliation: Graduate School of Peking Union Medical College, Beijing 100730, China; National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Guangqing
authors.initials: G
authors.lastname: Lu
authors.affiliation: Graduate School of Peking Union Medical College, Beijing 100730, China; National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Jinzhi
authors.initials: J
authors.lastname: Duan
authors.affiliation: Graduate School of Peking Union Medical College, Beijing 100730, China; National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Shu
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Xuxiang
authors.initials: X
authors.lastname: Wang
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Linlin
authors.initials: L
authors.lastname: Gao
authors.affiliation: Graduate School of Peking Union Medical College, Beijing 100730, China; National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.affiliation: Graduate School of Peking Union Medical College, Beijing 100730, China; National Institute of Biological Sciences, Beijing 102206, China zhangyu@nibs.ac.cn.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D004249:DNA Damage; D059766:DNA End-Joining Repair; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D051379:Mice; D014178:Translocation, Genetic
chemical_list: D007527:Isoenzymes; C000607894:Lig1 protein, mouse; D011088:DNA Ligases; D000072481:DNA Ligase ATP
keywords: DNA ligase; alternative end-joining; chromosome translocation; class switching recombination