Break dosage, cell cycle stage and DNA replication influence DNA double strand break response.
DNA double strand breaks (DSBs) can be repaired by non-homologous end joining (NHEJ) or homology-directed repair (HR). HR requires nucleolytic degradation of 5' DNA ends to generate tracts of single-stranded DNA (ssDNA), which are also important for the activation of DNA damage checkpoints. Here we describe a quantitative analysis of DSB processing in the budding yeast Saccharomyces cerevisiae. We show that resection of an HO endonuclease-induced DSB is less extensive than previously estimated and provide evidence for significant instability of the 3' ssDNA tails. We show that both DSB resection and checkpoint activation are dose-dependent, especially during the G1 phase of the cell cycle. During G1, processing near the break is inhibited by competition with NHEJ, but extensive resection is regulated by an NHEJ-independent mechanism. DSB processing and checkpoint activation are more efficient in G2/M than in G1 phase, but are most efficient at breaks encountered by DNA replication forks during S phase. Our findings identify unexpected complexity of DSB processing and its regulation, and provide a framework for further mechanistic insights.
Zierhut
Christian
C
Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, UK.
Diffley
John F X
JF
D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004261:DNA Replication; D018816:Genes, cdc; D008938:Mitosis; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000378:metabolism