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Nucleic Acids Res. 2013 Nov;41(21):9719-31. doi: 10.1093/nar/gkt729. Epub 2013 Aug 22.

Opposing roles for 53BP1 during homologous recombination.

Author information

1
DNA Double Strand Break Repair Laboratory, University of Sussex, Brighton BN1 9RQ, UK, Department of Biochemistry and Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Alberta T2N 4N1, Canada, Radiation Biology and DNA Repair Laboratory, Darmstadt University of Technology, 64287 Darmstadt, Germany and Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.

Abstract

Although DNA non-homologous end-joining repairs most DNA double-strand breaks (DSBs) in G2 phase, late repairing DSBs undergo resection and repair by homologous recombination (HR). Based on parallels to the situation in G1 cells, previous work has suggested that DSBs that undergo repair by HR predominantly localize to regions of heterochromatin (HC). By using H3K9me3 and H4K20me3 to identify HC regions, we substantiate and extend previous evidence, suggesting that HC-DSBs undergo repair by HR. Next, we examine roles for 53BP1 and BRCA1 in this process. Previous studies have shown that 53BP1 is pro-non-homologous end-joining and anti-HR. Surprisingly, we demonstrate that in G2 phase, 53BP1 is required for HR at HC-DSBs with its role being to promote phosphorylated KAP-1 foci formation. BRCA1, in contrast, is dispensable for pKAP-1 foci formation but relieves the barrier caused by 53BP1. As 53BP1 is retained at irradiation-induced foci during HR, we propose that BRCA1 promotes displacement but retention of 53BP1 to allow resection and any necessary HC modifications to complete HR. In contrast to this role for 53BP1 in HR in G2 phase, we show that it is dispensable for HR in S phase, where HC regions are likely relaxed during replication.

PMID:
23969417
PMCID:
PMC3834810
DOI:
10.1093/nar/gkt729
[Indexed for MEDLINE]
Free PMC Article

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