Proteasomal regulation of the mutagenic translesion DNA polymerase, Saccharomyces cerevisiae Rev1

Translesion DNA synthesis (TLS) functions as a tolerance mechanism for DNA damage at a potentially mutagenic cost. Three TLS polymerases (Pols) function to bypass DNA damage in Saccharomyces cerevisiae: Rev1, Pol zeta, a heterodimer of the Rev3 and Rev7 proteins, and Pol eta (Rad30). Our lab has shown that S. cerevisiae Rev1 protein levels are under striking cell cycle regulation, being similar to 50-fold higher during G2/M than during G1 and much of S phase (Waters and Walker, 2006). REV1 transcript levels only vary similar to 3-fold in a similar cell cycle pattern, suggesting a posttranscriptional mechanism controls protein levels. Here, we show that the S. cerevisiae Rev1 protein is unstable during both the G1 and the G2/M phases of the cell cycle, however, the protein's half-life is shorter in Cl arrested cells than in G2/M arrested cells, indicating that the rate of proteolysis strongly contributes to Rev1's cell cycle regulation. In the presence of the proteasome inhibitor, MG132, the steady-state levels and half-life of Rev1 increase during Cl and G2/M. Through the use of a viable proteasome mutant, we confirm that the levels of Rev1 protein are dependent on proteasome-mediated degradation. The accumulation of higher migrating forms of Rev1 under certain conditions shows that the degradation of Rev1 is possibly directed through the addition of a polyubiquitination signal or another modification. These results support a model that proteasomal degradation acts as a regulatory system of mutagenic TLS mediated by Rev1. (C) 2010 Elsevier B.V. All rights reserved.