BE-FLARE: A Fluorescent Reporter of Base Editing Activity Reveals Editing Characteristics of APOBEC3A and APOBEC3B

Base Editing is a precise genome editing method that uses a deaminase-Cas9 fusion protein to mutate cytidine to thymidine in target DNA in situ without the generation of a double-strand break. We have developed a Base Editing FLuorescent Activity REporter (BE-FLARE), which allows for enrichment of cells that have undergone editing of target loci, and is superior to a co-expressed marker. Although base editors conventionally use rat APOBEC1 as the cytidine deaminase component, we use the activity reporter to analyse the editing efficiency of additional APOBEC family members and identified human APOBEC3A and APOBEC3B as highly efficient cytidine deaminases for base editing applications with unique properties. Using these advances, we outline workflows for accelerated generation of genetically engineered cells.