DNA Polymerase β Bypasses in vitro a Single d(GpG)-Cisplatin Adduct Placed on Codon 13 of the HRAS Gene

We have examined the capacity of calf thymus DNA polymerases α, β, δ, and ε to perform in vitro translesion synthesis on a substrate containing a single d(GpG)-cisplatin adduct placed on codon 13 of the human HRAS gene. We found that DNA synthesis catalyzed by DNA polymerases α, δ, and ε was blocked at the base preceding the lesion. Addition of proliferating cell nuclear antigen to DNA polymerase δ and replication protein A to DNA polymerase α did not restore their capacity to elongate past the adduct. On the other hand, DNA polymerase β efficiently bypassed the cisplatin adduct. Furthermore, we observed that DNA polymerase β was the only polymerase capable of primer extension of a 3'-OH located opposite the base preceding the lesion. Likewise, DNA polymerase β was able to elongate the arrested replication products of the other three DNA polymerases, thus showing its capacity to successfully compete with polymerases α, δ, and ε in the stalled replication complex. Our data suggest (i) a possible mechanism enabling DNA polymerase β to bypass a d(GpG)-cisplatin adduct in vitro and (ii) a role for this enzyme in processing DNA damage in vivo.