Abstract: Some aspects of this disclosure provide strategies, systems, reagents, methods, and kits that are useful for the targeted editing of nucleic acids or the modification of nucleic acids or proteins, including editing a single site within the genome of a cell or subject, e.g., within the human genome. In some embodiments, fusion proteins of nucleic acid programmable DNA binding proteins e.g., GeoCas9 or variants thereof, and effector domains, e.g., deaminase domains, are provided. In some embodiments, methods for targeted nucleic acid editing or protein modification are provided. In some embodiments, reagents and kits for the generation of targeted nucleic acid editing proteins, e.g., fusion proteins of a GeoCas9 and effector domains, are provided.