![]() Recently, Huang and colleagues described circularly permuted base editors in Streptococcus pyogenes Cas9 (SpCas9) and found that they had comparable on-target activity compared to their uncircularized counterparts 12. To date, these strategies are effective at improving the biosafety of ABEs but represent a Cas9-independent solution toward minimizing aberrant editing. Despite their broad scope for robust on-target editing, non-engineered ABEs have a significant off-target footprint on the transcriptome and effect incidences of missense and nonsense mutations 8.Įfforts to minimize the occurrence of promiscuous editing have largely improved the fidelity of existing ABEs by installing various inactivating mutations in the wild-type domain of the ecTadA monomer 9, or use truncated variants of ABEmax with amino acid substitution to reduce non-specific contacts with RNA in the recently described, miniABEmax, which consists of a single, evolved ecTadA monomer 10, 11. Current generation adenine base editors (ABEs) employ a dimerized, codon optimized variant of laboratory-evolved ecTadA (ABEmax) 4, 5, and have directed site-specific adenine-to-guanine nucleotide conversions in a diverse array of systems 6, 7. ![]() ![]() ![]() Cytosine base editors (CBEs) direct cytosine-to-thymine chemistry at a user-defined guide sequence (sgRNA) 1, 2, and comprise a cytosine deaminase derived from vertebrate (APOBEC and activation-induced deaminase variants) 3 or invertebrate systems (pmCDA1 Target-AID) 2. ![]()
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