Error-free replicative bypass of (6-4) photoproducts by DNA polymerase zeta in mouse and human cells

Abstract

The ultraviolet (UV)-induced (6-4) pyrimidine-pyrimidone photoproduct [(6-4) PP] confers a large structural distortion in DNA. Here we examine in human cells the roles of translesion synthesis (TLS) DNA polymerases (Pols) in promoting replication through a (6-4) TT photoproduct carried on a duplex plasmid where bidirectional replication initiates from an origin of replication. We show that TLS contributes to a large fraction of lesion bypass and that it is mostly error-free. We find that, whereas Pol eta and Pol iota provide alternate pathways for mutagenic TLS, surprisingly, Pol zeta functions independently of these Pols and in a predominantly error-free manner. We verify and extend these observations in mouse cells and conclude that, in human cells, TLS during replication can be markedly error-free even opposite a highly distorting DNA lesion.

Figure 1.

Pathways for replicative bypass of (6–4) photoproducts in human and mouse cells. Pol η, Pol ι, and Pol ζ provide three alternate routes of TLS. Following nucleotide insertion opposite the 3′ T or 3′ C of the (6–4) photoproduct by either Pol η or by Pol ι, an as-yet-unidentified Pol would extend, and TLS by these Pols is primarily responsible for the mutational events. In Pol ζ-mediated TLS, following nucleotide insertion opposite the 3′ T or 3′ C by a Pol that remains to be identified, Pol ζ would carry out the extension reaction, and this pathway is largely error-free.