Base Editing: Chemistry on the Genome

Genome editing methods have commonly relied on the initial introduction of double‐stranded DNA breaks (DSBs), resulting in stochastic insertions, deletions, and translocations at the target genomic locus. To achieve gene correction, these methods typically require the introduction of exogenous DNA repair templates and low‐efficiency homologous recombination processes. Here I describe the development of base editing, a new approach to genome editing that enables the direct, irreversible conversion of one target DNA base into another in a programmable manner, without requiring double‐stranded DNA backbone cleavage or a donor template. Base editors employ single‐stranded DNA‐specific deaminase enzymes tethered to a catalytically impaired Cas9 protein (dCas9) to directly chemically convert thymines to uracils or adenines to inosines in the genome. These chemoselective genomic modifications efficiently and cleanly result in permanent C•G to T•A or T•A to C•G correction in living cells and organisms.C•G to T•A base editing overview. DNA with a target C (red) at a locus specified by a guide RNA (green) is bound by dCas9 (blue), which mediates local DNA strand separation. Cytidine deamination by a tethered APOBEC1 enzyme (red) converts the single‐stranded target C→U. The resulting G:U heteroduplex can be permanently converted to an A:T base pair following DNA replication or DNA repair.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .