Abstract
The distribution of DNA damage and repair is considered to occur heterogeneously across the genome. However, commonly available techniques, such as the alkaline comet assay or HPLC-MS/MS, measure global genome levels of DNA damage, and do not reflect potentially significant events occurring at the gene/sequence-specific level, in the nuclear or mitochondrial genomes. We developed a method, which comprises a combination of Damaged DNA Immunoprecipitation and next generation sequencing (DDIP-seq), to assess the induction and repair of DNA damage induced by 0.1 J/cm
solar-simulated radiation at the sequence-specific level, across both the entire nuclear and mitochondrial genomes. DDIP-seq generated a genome-wide, high-resolution map of cyclobutane thymine dimer (TT) location and intensity. In addition to being a straightforward approach, our results demonstrated a clear differential distribution of TT induction and loss, across both the nuclear and mitochondrial genomes. For nuclear DNA, this differential distribution existed at both the sequence and chromosome level. Levels of TT were much higher in the mitochondrial DNA, compared to nuclear DNA, and decreased with time, confirmed by qPCR, despite no reported mechanisms for their repair in this organelle. These data indicate the existence of regions of sensitivity and resistance to damage formation, together with regions that are fully repaired, and those for which > 90% of damage remains, after 24 h. This approach offers a simple, yet more detailed approach to studying cellular DNA damage and repair, which will aid our understanding of the link between DNA damage and disease.