Engineering a bacterial toxin deaminase from the DYW-family into a novel cytosine base editor for plants and mammalian cells

Base editors are precise editing tools that employ deaminases to modify target DNA bases. The DYW-family of cytosine deaminases is structurally and phylogenetically distinct and might be harnessed for genome editing tools. We report a novel CRISPR/Cas9-cytosine base editor using SsdA, a DYW-like deaminase and bacterial toxin. A G103S mutation in SsdA enhances C-to-T editing efficiency while reducing its toxicity. Truncations result in an extraordinarily small enzyme. The SsdA-base editor efficiently converts C-to-T in rice and barley protoplasts and induces mutations in rice plants and mammalian cells. The engineered SsdA is a highly efficient genome editing tool.