Nanopore Sequencing Accurately Identifies the Mutagenic DNA Lesion O; 6; -Carboxymethyl Guanine and Reveals Its Behavior in Replication

O; 6; -carboxymethylguanine (O; 6; -CMG) is a highly mutagenic alkylation product of DNA, triggering transition mutations relevant to gastrointestinal cancer. However, precise localization of a single O; 6; -CMG with conventional sequencing platforms is challenging. Here nanopore sequencing (NPS), which directly senses single DNA bases according to their physiochemical properties, was employed to detect O; 6; -CMG. A unique O; 6; -CMG signal was observed during NPS and a single-event call accuracy of >95 % was achieved. Moreover, O; 6; -CMG was found to be a replication obstacle for Phi29 DNA polymerase (Phi29 DNAP), suggesting this lesion could cause DNA sequencing biases in next generation sequencing (NGS) approaches.