Design and analysis of site-specific single-strand nicking endonucleases for gene correction

Single-strand nicking endonucleases ("nickases") have been shown to induce homology-mediated gene correction with reduced toxicity of DNA double-strand break-producing enzymes, and nickases have been engineered from both homing endonuclease and FokI-based scaffolds. We describe the strategies used to engineer these site-specific nickases as well as the in vitro methods used to confirm their activity and specificity. Additionally, we describe the Traffic Light Reporter system, which uses a flow cytometric assay to simultaneously detect both gene repair and mutagenic nonhomologous end-joining outcomes at a single targeted site in mammalian cells. With these methods, novel nickases can be designed and tested for use in gene correction with novel target sites.