Long-range DNA end resection supports homologous recombination by checkpoint activation rather than extensive homology generation

Homologous recombination (HR), the error-free mechanism for double-strand break (DSB) repair, relies on DNA end resection by nucleolytic degradation of the 5′-terminated ends. However, the role of long-range resection mediated by Exo1 and/or Sgs1-Dna2 in HR is not fully understood. Here, we show that Exo1 and Sgs1 are dispensable for recombination between closely-linked repeats but are required for interchromosomal repeat recombination inSaccharomyces cerevisiae. This requirement for long-range resection is coupled to DNA damage checkpoint activation and the need for checkpoint proteins. Furthermore, artificial activation of the checkpoint partially restores interchromosomal recombination toexo1Δ sgs1Δcells. However, cell cycle delay is insufficient to rescue the interchromosomal recombination defect ofexo1Δ sgs1Δcells, suggesting an additional role for the checkpoint. Given that the checkpoint is necessary for DNA damage-induced chromosome mobility, we propose that the importance of the checkpoint, and therefore long-range resection, in interchromosomal recombination is due to a need to increase chromosome mobility to facilitate pairing of distant sites. The need for long-range resection is circumvented when the DSB and its repair template are in close proximity.