a) Diagram of AID variants. NLS, NES, deaminase domain, truncations, and activity-altering mutations are indicated. b) Fluorescence microscopy of MS2-AID and MS2-AIDΔ constructs in K562 cells is shown. Cells were fixed and stained with an MS2 antibody (green) and the nuclear stain DAPI (blue). c) A comparison of the expression of different MS2-AID variants is shown. K562 cells expressing the variants were lysed and analyzed on an SDS-PAGE gel followed by immunoblotting with an MS2 antibody (top) or GAPDH antibody (bottom). d) K562 cells containing dCas9, GFP, and mCherry were transiently electroporated with indicated combinations of MS2-AID, MS2-AIDΔ, or MS2-AIDΔDead and either sgGFP.1 or sgNegCtrl. GFP and mCherry fluorescence of the cells were measured by flow cytometry as a proxy for mutation rate. Shown are the scatter plots from the flow cytometry and a graph summarizing the non-fluorescent populations. e) Cells were sorted for low GFP expression and the GFP locus was sequenced. A graph of the enrichment of mutation at each base is shown here.