| Summary: | Summary: Although double-strand break (DSB) repair is essential for a cell’s survival, little is known about how DSB repair mechanisms are affected by age. Here we characterize the impact of cellular aging on the efficiency of single-strand annealing (SSA), a DSB repair mechanism. We measure SSA repair efficiency in young and old yeast cells and report a 23.4% decline in repair efficiency. This decline is not due to increased use of non-homologous end joining. Instead, we identify increased G1 phase duration in old cells as a factor responsible for the decreased SSA repair efficiency. Expression of 3xCLN2 leads to higher SSA repair efficiency in old cells compared with expression of 1xCLN2, confirming the involvement of cell-cycle regulation in age-associated repair inefficiency. Examining how SSA repair efficiency is affected by sequence heterology, we find that heteroduplex rejection remains high in old cells. Our work provides insights into the links between single-cell aging and DSB repair efficiency. : Young et al. demonstrate that the efficiency of double-strand break repair by single-strand annealing (SSA) declines with replicative age in yeast cells. This decline is associated with changes in cell-cycle progression and not due to increased use of non-homologous end joining. Heteroduplex rejection due to a 3% mismatch in SSA repair substrates does not decline with replicative age. Keywords: aging, systems biology, DNA repair, double-strand break, replicative lifespan, single cell, yeast, single-strand annealing, microscopy, microfluidics
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