No abstract

A double -strand break (DSB) is one of the most deleterious forms of DNA damage. In eukaryotic cells, two main repair pathways have evolved to repair DSBs, homologous recombination (HR) and non-homologous end-joining (NHEJ). During replicative aging in the unicellular eukaryotic organism, S. cerevisiae, the relative use of HR and NHEJ shifts in favor of end-joining repair. By monitoring repair events in the HO-DSB system, we show that DNA resection decreased early in replicative aging as did the recovery of long-range resection factors, Dna2-Sgs1 and Exo1. As aging progressed, the retention of Ku70 then decreased and irreparable DSBs accumulated with the pore complex at the nuclear periphery. End-bridging remained intact as HR and NHEJ declined, but eventually it became disrupted in cells of older replicative age. In all, our work provides insight about age-related molecular changes in DSB repair, where both canonical pathways become disrupted. HR declines first, leading to a transient reliance on NHEJ, which then also declines as cells repair through a mechanism yielding products with larger deletions and 1-2bp of microhomologies at break junctions.