Simultaneous Disruption of Two DNA Polymerases, Polη and Polζ, in Avian DT40 Cells Unmasks the Role of Polη in Cellular Response to Various DNA Lesions

Replicative DNA polymerases are frequently stalled by DNA lesions. The resulting replication blockage is released by homologous recombination (HR) and translesion DNA synthesis (TLS). TLS employs specialized TLS polymerases to bypass DNA lesions. We provide striking in vivo evidence of the cooperation between DNA polymerase eta, which is mutated in the variant form of the cancer predisposition disorder xeroderma pigmentosum (XP-V), and DNA polymerase zeta by generating POL eta(-/-) /POL zeta(-/-) cells from the chicken DT40 cell line. POL zeta(-/-) cells are hypersensitive to a very wide range of DNA damaging agents, whereas XP-V cells exhibit moderate sensitivity to ultraviolet light (UV) only in the presence of caffeine treatment and exhibit no significant sensitivity to any other damaging agents. It is therefore widely believed that Pol eta plays a very specific role in cellular tolerance to UV-induced DNA damage. The evidence we present challenges this assumption. The phenotypic analysis of POL eta(-/-) /POL zeta(-/-) cells shows that, unexpectedly, the loss of Pol eta significantly rescued all mutant phenotypes of POL zeta(-/-) cells and results in the restoration of the DNA damage tolerance by a backup pathway including HR. Taken together, Pol eta contributes to a much wide range of TLS events than had been predicted by the phenotype of XP-V cells.