PCR was performed using Q5 Hot Start High-Fidelity DNA Polymerase (New England Biolabs). Plasmids for BE and sgRNA were constructed using USER cloning (New England Biolabs) from previously reported plasmids1 (link). DNA vector amplification was carried out using NEB 10beta competent cells (New England Biolabs). Site-directed mutagenesis of APOBEC1 variants was done using blunt-end ligation. Briefly, a primer with an overhang containing the desired point mutation was used to amplify the appropriate vector plasmid by PCR. KLD enzyme mix (New England Biolabs) was used to phosphorylate and circularize the PCR product prior to transformation.