Mitotic DNA synthesis is caused by transcription-replication conflicts in BRCA2-deficient cells

Mol Cell. 2022 Sep 15;82(18):3382-3397.e7. doi: 10.1016/j.molcel.2022.07.011. Epub 2022 Aug 23.


Aberrant replication causes cells lacking BRCA2 to enter mitosis with under-replicated DNA, which activates a repair mechanism known as mitotic DNA synthesis (MiDAS). Here, we identify genome-wide the sites where MiDAS reactions occur when BRCA2 is abrogated. High-resolution profiling revealed that these sites are different from MiDAS at aphidicolin-induced common fragile sites in that they map to genomic regions replicating in the early S-phase, which are close to early-firing replication origins, are highly transcribed, and display R-loop-forming potential. Both transcription inhibition in early S-phase and RNaseH1 overexpression reduced MiDAS in BRCA2-deficient cells, indicating that transcription-replication conflicts (TRCs) and R-loops are the source of MiDAS. Importantly, the MiDAS sites identified in BRCA2-deficient cells also represent hotspots for genomic rearrangements in BRCA2-mutated breast tumors. Thus, our work provides a mechanism for how tumor-predisposing BRCA2 inactivation links transcription-induced DNA damage with mitotic DNA repair to fuel the genomic instability characteristic of cancer cells.

Keywords: BRCA2; MiDAS; R-loops; TRCs; genome stability; mitotic DNA synthesis; transcription-replication conflicts.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aphidicolin / pharmacology
  • BRCA2 Protein / genetics
  • Chromosome Fragile Sites / genetics
  • DNA / genetics
  • DNA Damage
  • DNA Replication*
  • Genomic Instability
  • Humans
  • Mitosis* / genetics


  • BRCA2 Protein
  • BRCA2 protein, human
  • Aphidicolin
  • DNA