The title in Nature: “Programmable base editing of A•T to G•C in genomic DNA without DNA cleavage” A brief description of what was accomplished (a modification

The title in Nature: “Programmable base editing of A•T to G•C in genomic DNA without DNA cleavage” A brief description of what was accomplished (a modification of cas9): “We evolved a tRNA adenosine deaminase to operate on DNA when fused to a catalytically impaired CRISPR-Cas9. Extensive directed evolution and protein engineering resulted in seventh-generation ABEs (e.g., ABE7.10), that convert target A•T to G•C base pairs efficiently (~50% in human cells) with very high product purity (typically ≥ 99.9%) and very low rates of indels (typically ≤ 0.1%).“ Translation: they modified the CRISPR associated DNA editing enzyme, cas9, to “deaminate” (remove or otherwise alter the amino groups) in A-T or G-C pairs without breaking the DNA, as cas9 normally would. This makes single point precision edits possible, but I’m not sure what that implies for the “guide RNA” cas9 needs to know where to make the edits, as I haven’t read the paper in full yet.