Frameshifts and deletions during in vitro translesion synthesis past Pt-DNA adducts by DNA polymerases β and η

DNA polymerases beta (pol beta) and eta (pol eta) are the only two eukaryotic polymerases known to efficiently bypass cisplatin and oxaliplatin adducts in vitro. Frameshift errors are an important aspect of mutagenesis. We have compared the types of frameshifts that occur during translesion synthesis past cisplatin and oxaliplatin adducts in vitro by pol beta and pol eta on a template containing multiple runs of nucleotides flanking a single platinum-GG adduct. Translesion synthesis past platinum adducts by pol beta resulted in approximately 50% replication products containing single-base deletions. For both adducts the majority of -1 frameshifts occurred in a TTT sequence 3-5 bp upstream of the DNA lesion. For pol eta, all of the bypass products for both cisplatin and oxaliplatin adducts contained - I frameshifts in the upstream TTT sequence and most of the products of replication on oxaliplatin-damaged templates had multiple replication errors, both frameshifts and misinsertions. In addition, on platinated. templates both polymerases generated replication products 4-8 bp shorter than the full-length products. The majority of short cisplatin-induced products contained an internal deletion which included the adduct. In contrast, the majority of oxaliplatin-induced short products contained a 3' terminal deletion. The implications of these in vitro results for in vivo mutagenesis are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.