First, we compared ERC levels in wild type and fob1Δ cells. A modest increase in all three species of ERCs was evident in wild type cells after aging replicatively for 26 hours, a relatively young age when the population maintains ∼90% viability (Figure 1A and [16]). As the population approaches its median RLS by 50 hours, ERC levels continued to increase dramatically. Similar to previous reports, in relatively young cells, ERC levels in a fob1Δ diploid were low compared to wild type cells (Figure 8B and [42]), but their accumulation was not completely prevented. After 26 hours of replicative aging, total ERC levels in the fob1Δ strain had increased ∼5-fold above young wild type levels, but were still reduced ∼50% compared to the age-matched wild type population. Interestingly, as the fob1Δ population continued to age, ERC accumulation continued: Total ERC levels in fob1Δ cells were still ∼50% lower than wild type cells after aging replicatively for 50 hours, but by this age ERC levels in the fob1Δ strain had increased ∼17-fold above young wild type levels. These results indicate that
