Homologous recombination and nonhomologous end-joining repair pathways regulate fragile site stability

Michal Schwartz, Eitan Zlotorynski, Michal Goldberg, Efrat Ozeri, Ayelet Rahat, Carlos Le Sage, Benjamin P.C. Chen, David J. Chen, Reuven Agami, Batsheva Kerem*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

116 Scopus citations


Common fragile sites are specific loci that form gaps and constrictions on metaphase chromosomes exposed to replication stress, which slows DNA replication. These sites have a role in chromosomal rearrangements in tumors; however, the molecular mechanism of their expression is unclear. Here we show that replication stress leads to focus formation of Rad51 and phosphorylated DNA-PKcs, key components of the homologous recombination (HR) and nonhomologous end-joining (NHEJ), double-strand break (DSB) repair pathways, respectively. Down-regulation of Rad51, DNA-PKcs, or Ligase IV, an additional component of the NHEJ repair pathway, leads to a significant increase in fragile site expression under replication stress. Replication stress also results in focus formation of the DSB markers, MDC1 and γH2AX. These foci colocalized with those of Rad51 and phospho-DNA-PKcs. Furthermore, γH2AX and phospho-DNA-PKcs foci were localized at expressed fragile sites on metaphase chromosomes. These findings suggest that DSBs are formed at common fragile sites as a result of replication perturbation. The repair of these breaks by both HR and NHEJ pathways is essential for chromosomal stability at these sites.

Original languageAmerican English
Pages (from-to)2715-2726
Number of pages12
JournalGenes and Development
Issue number22
StatePublished - 15 Nov 2005


  • Common fragile sites
  • Double-strand breaks
  • Genomic instability
  • Homologous recombination
  • Nonhomologous end-joining
  • Replication stress


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