Described herein are methods and compositions for improving the genome-wide specificities of targeted base editing technologies. Herein, we describe dimeric base editing (BE) technologies that use split deaminases (sDA) that are functional when brought into close proximity to each other, one fused to a ZF and one to an nCas9-UGI protein comprising one or more UGIs, so as to limit the ability of the deaminase domain from deaminating at off-target ssDNA target sites independent of nCas9 R-loop formation. Thus, provided herein are fusion proteins comprising: (i) a first portion of a split deaminase ("sDAI") enzyme fused to a programmable DNA-binding domain； or (ii) a second portion of a split deaminase ("sDA2") fused to an nCas9 protein. The present invention also includes the vectors and cells comprising the vectors, as well as kits comprising the proteins and nucleic acids described herein.
