Precise mapping of single-stranded DNA breaks by using an engineered, error-prone DNA polymerase for sequence-templated erroneous end-labelling

The ability to analyze whether DNA includes lesions is important in identifying mitogenic substances. Until now, the detection of single-stranded DNA breaks (SSBs) has lacked precise methods. To overcome this limitation, we have engineered a chimeric DNA polymerase, Sloppymerase, that is able to replicate DNA in the absence of one nucleotide. In addition to polymerase activity, Sloppymerase demonstrates 5´-3´exonuclease activity. We characterized the activity of Sloppymerase and utilized the enzyme to develop a method for sequence-templated erroneous end-labelling sequencing (STEEL-seq) that is relevant to the mapping of SSBs. Following the omission of a specific nucleotide, e.g., dATP, from the reaction mixture, Sloppymerase introduces mismatches directly downstream of SSBs at positions that should contain deoxyadenosine. The ability to retain sequence information after end-labelling ensures that hits are bona fide SSBs. STEEL-seq works with a variety of sequencing technologies, shown by our successful experiments using Sanger, Illumina, PacBio and Nanopore systems.