Abstract
Eukaryotic genomes are duplicated by a complex machinery, utilizing high fidelity replicative B-family DNA polymerases (pols) alpha, delta and epsilon. Specialized error-prone pol zeta, the fourth B-family member, is recruited when DNA synthesis by the accurate trio is impeded by replication stress or DNA damage. The damage tolerance mechanism dependent on pol prevents DNA/genome instability and cell death at the expense of increased mutation rates. The pol switches occurring during this specialized replication are not fully understood. The loss of pol zeta results in the absence of induced mutagenesis and suppression of spontaneous mutagenesis. Disruption of the Fe-S cluster motif that abolish the interaction of the C-terminal domain (CID) of the catalytic subunit of pol with its accessory subunits, which are shared with pol delta, leads to a similar defect in induced mutagenesis. Intriguingly, the po13-13 mutation that affects the Fe-S cluster in the CTD of the catalytic subunit of pol 8 also leads to defective induced mutagenesis, suggesting the possibility that Fe-S clusters are essential for the pol switches during replication of damaged DNA. We confirmed that yeast strains with the po13-13 mutation are UV-sensitive and defective in UV-induced mutagenesis. However, they have increased spontaneous mutation rates. We found that this increase is dependent on functional pol zeta. In the p013-13 mutant strain with defective pol 8, there is a sharp increase in transversions and complex mutations, which require functional pol zeta, and an increase in the occurrence of large deletions, whose size is controlled by pol C. Therefore, the pol3-13 mutation abrogates pol c-dependent induced mutagenesis, but allows for pol C recruitment for the generation of spontaneous mutations and prevention of larger deletions. These results reveal differential control of the two major types of pol c-dependent mutagenesis by the Fe-S cluster present in replicative pol delta. (C) 2016 Elsevier B.V. All rights reserved.