Nanopore Sequencing Accurately Identifies the Mutagenic DNA Lesion O6 -Carboxymethyl Guanine and Reveals Its Behavior in Replication.

O6 -carboxymethylguanine (O6 -CMG) is a highly mutagenic alkylation product of DNA, triggering transition mutations relevant to gastrointestinal cancer. However, precise localization of a single O6 -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 O6 -CMG. A unique O6 -CMG signal was observed during NPS and a single-event call accuracy of >95 % was achieved. Moreover, O6 -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.