Originally published as Genetics Published Articles Ahead of Print on October 19, 2009.

Genetics, Vol. 184, 27-42, January 2010, Copyright © 2010
doi:10.1534/genetics.109.107482

Participation of DNA Polymerase {zeta} in Replication of Undamaged DNA in Saccharomyces cerevisiae

Matthew R. Northam, Heather A. Robinson1, Olga V. Kochenova2 and Polina V. Shcherbakova3

Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198

3 Corresponding author: University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, NE 68198.
E-mail: pshcherb{at}unmc.edu

Translesion synthesis DNA polymerases contribute to DNA damage tolerance by mediating replication of damaged templates. Due to the low fidelity of these enzymes, lesion bypass is often mutagenic. We have previously shown that, in Saccharomyces cerevisiae, the contribution of the error-prone DNA polymerase {zeta} (Pol{zeta}) to replication and mutagenesis is greatly enhanced if the normal replisome is defective due to mutations in replication genes. Here we present evidence that this defective-replisome-induced mutagenesis (DRIM) results from the participation of Pol{zeta} in the copying of undamaged DNA rather than from mutagenic lesion bypass. First, DRIM is not elevated in strains that have a high level of endogenous DNA lesions due to defects in nucleotide excision repair or base excision repair pathways. Second, DRIM remains unchanged when the level of endogenous oxidative DNA damage is decreased by using anaerobic growth conditions. Third, analysis of the spectrum of mutations occurring during DRIM reveals the characteristic error signature seen during replication of undamaged DNA by Pol{zeta} in vitro. These results extend earlier findings in Escherichia coli indicating that Y-family DNA polymerases can contribute to the copying of undamaged DNA. We also show that exposure of wild-type yeast cells to the replication inhibitor hydroxyurea causes a Pol{zeta}-dependent increase in mutagenesis. This suggests that DRIM represents a response to replication impediment per se rather than to specific defects in the replisome components.