Sgs1 and Esc2 suppress chromosome translocations induced by a replication fork barrier in Saccharomyces cerevisiae

Replication stress is recognized as a major cause of genomic instability in eukaryotes and is associated with various human pathologies, including cancer. To investigate the mechanisms driving gross chromosomal rearrangements in response to replication stress, we used the bacterial Tus/Ter barrier to engineer a site-specific replication fork block in the Saccharomyces cerevisiae genome. Surprisingly, we find that replication fork stalling adjacent to a region sharing homology with other chromosomes only modestly induces translocations in wild-type cells. However, the frequency of chromosome translocations is greatly increased in the absence of Sgs1 or Esc2. We show that the elevated frequency of Tus/Ter-induced translocations in sgs1Δ and esc2Δ mutants is completely dependent on RAD51, consistent with their formation by homologous recombination. In addition, we find that Exo1 nuclease contributes to the high frequency of chromosome translocations observed in sgs1Δ and esc2Δ cells, while the Mph1 translocase participates in replication stress-induced GCRs mostly in the absence of Esc2. Based on our findings, we propose that different factors contribute positively or negatively to the formation of chromosomal rearrangements associated with replication stress.