Biochemical reconstitution of UV-induced mutational processes.

Tomohiko Sugiyama,Yizhang Chen

doi:10.1093/nar/gkz335

Abstract

We reconstituted two biochemical processes that may contribute to UV-induced mutagenesis in vitro and analysed the mutational profiles in the products. One process is translesion synthesis (TLS) by DNA polymerases (Pol) δ, η and ζ, which creates C>T transitions at pyrimidine dimers by incorporating two dAMPs opposite of the dimers. The other process involves spontaneous deamination of cytosine, producing uracil in pyrimidine dimers, followed by monomerization of the dimers by secondary UV irradiation, and DNA synthesis by Pol δ. The mutational spectrum resulting from deamination without translesion synthesis is similar to a mutational signature found in melanomas, suggesting that cytosine deamination encountered by the replicative polymerase has a prominent role in melanoma development. However, CC>TT dinucleotide substitution, which is also commonly observed in melanomas, was produced almost exclusively by TLS. We propose that both TLS-dependent and deamination-dependent mutational processes are likely involved in UV-induced melanoma development.

Highlights

A major cause of skin cancer, ultraviolet light (UV)-induced DNA damage has been studied in great detail ((1,2) for reviews)
A 99-mer singlestranded DNA (ssDNA) molecule was irradiated with UV and hybridized with 32Plabeled primer and mixed with yeast Pol ␦ to initiate primer extension
We found only minor increases in single nucleotide insertions and deletions produced in the presence of hPol ␩ + yPol ␨ on UVB

Summary

Introduction

A major cause of skin cancer, ultraviolet light (UV)-induced DNA damage has been studied in great detail ((1,2) for reviews). The major DNA photoproducts produced by UV radiation are dimers of two adjacent pyrimidines (pyrimidine dimers) that include cyclobutane pyrimidine dimers (CPD), [] photoproducts and their Dewar isomers. While most of these photoproducts are repaired by nucleotide excision repair (NER) in cells, unrepaired damage may lead to DNA mutation. More than 90% of mutations in Signature 7 are CG-pair to TA-pair transitions (C>T transitions) in contiguous pyrimidine residues [5], supporting that the majority of the mutations occur at the pyrimidine dimers

Methods

Results

Conclusion