Harnessing TLS polymerases to direct nucleotide outcomes in base editing

Base editors introduce defined DNA lesions rather than directly rewriting nucleotides, and these lesions must be processed by cellular DNA repair pathways. In glycosylase-mediated base editing, apurinic/apyrimidinic sites (AP sites) represent a critical decision point where the choice of repair pathway determines whether the outcome is a desired substitution or an unintended byproduct. Although product heterogeneity has long been considered an intrinsic limitation of base editing, recent mechanistic studies suggest competition among repair polymerases represents a major contributor. Evidence indicates translesion synthesis polymerases can serve as tunable resolvers by preferentially inserting specific nucleotides opposite AP sites. Engineering their recruitment and insertion preferences may shift base editing from a stochastic repair-dependent process toward a more predictable mode of nucleotide incorporation.