The gerontogene Sir2p is required for active retention of damaged proteins during cytokinesis.
Nika Erjavec, Thomas Nyström
CMB Microbiology, Gothenburg University, Medicinaregatan 9c, Gothenburg, 40530, Sweden
Aging in different organisms has been associated with the accumulation of several genetic and physiological modifications, including damaged proteins. In the yeast Saccharomyces cerevisiae, the latter are segregated to the mother cell during division, in what is believed to ensure a full replicative potential of the offspring. However, as oxidized proteins increase with age, they are progressively inherited also by the bud. Loss of asymmetry is a hallmark of the short-lived sir2 Δ mutant. Here we show that aging affects indiscriminately the most abundant proteins in old wild-type cells, but has a strong bias towards chaperones in age-matched sir2 Δ cells. Asymmetric segregation only targets the damaged form of a protein, since the protein levels are equal between mother and bud. We also show that such distribution is not achieved by way of a higher specific rate of synthesis in the bud; and thereby suggest it is the result of active retention in the mother. We hence propose a role for Sir2p in the retention of oxidized proteins during cytokinesis, possibly through the concerted action of chaperones and actin filaments.