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J Cell Biol. 2013 Jan 21;200(2):173-86. doi: 10.1083/jcb.201203128.

A noncatalytic function of the ligation complex during nonhomologous end joining.

Author information

1
Centre National de la Recherche Scientifique, Institut de Pharmacologie et de Biologie Structurale, Toulouse F-31077, Cedex 4, France.

Abstract

Nonhomologous end joining is the primary deoxyribonucleic acid (DNA) double-strand break repair pathway in multicellular eukaryotes. To initiate repair, Ku binds DNA ends and recruits the DNA-dependent protein kinase (DNA-PK) catalytic subunit (DNA-PKcs) forming the holoenzyme. Early end synapsis is associated with kinase autophosphorylation. The XRCC4 (X4)-DNA Ligase IV (LIG4) complex (X4LIG4) executes the final ligation promoted by Cernunnos (Cer)-X4-like factor (XLF). In this paper, using a cell-free system that recapitulates end synapsis and DNA-PKcs autophosphorylation, we found a defect in both activities in human cell extracts lacking LIG4. LIG4 also stimulated the DNA-PKcs autophosphorylation in a reconstitution assay with purified components. We additionally uncovered a kinase autophosphorylation defect in LIG4-defective cells that was corrected by ectopic expression of catalytically dead LIG4. Finally, our data support a contribution of Cer-XLF to this unexpected early role of the ligation complex in end joining. We propose that productive end joining occurs by early formation of a supramolecular entity containing both DNA-PK and X4LIG4-Cer-XLF complexes on DNA ends.

PMID:
23337116
PMCID:
PMC3549972
DOI:
10.1083/jcb.201203128
[Indexed for MEDLINE]
Free PMC Article

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