Replicative polymerases (Pols) arrest at damaged
DNA nucleotides, which induces ubiquitination of the
DNA sliding clamp
PCNA (
PCNA-Ub) and DNA damage signaling.
PCNA-Ub is associated with the recruitment or activation of translesion synthesis (TLS)
DNA polymerases of the Y family that can bypass the lesions, thereby rescuing replication and preventing replication fork collapse and consequent formation of double-strand DNA breaks. Here, we have used gene-targeted mouse embryonic fibroblasts to perform a comprehensive study of the in vivo roles of
PCNA-Ub and of the Y family TLS Pols η, ι, κ, Rev1 and the B family TLS Polζ in TLS and in the suppression of DNA damage signaling and
genome instability after exposure to UV light. Our data indicate that TLS Pols ι and κ and the N-terminal BRCT domain of Rev1, that previously was implicated in the regulation of TLS, play minor roles in TLS of
DNA photoproducts.
PCNA-Ub is critical for an early TLS pathway that replicates both strongly helix-distorting (6-4)
pyrimidine-
pyrimidone ((6-4)PP) and mildly distorting
cyclobutane pyrimidine dimer (CPD) photoproducts. The role of Polη is mainly restricted to early TLS of CPD photoproducts, whereas Rev1 and, in particular, Polζ are essential for the bypass of (6-4)PP photoproducts, both early and late after exposure. Thus, structurally distinct photoproducts at the mammalian genome are bypassed by different TLS Pols in temporally different,
PCNA-Ub-dependent and independent fashions.