The "new favorite" of gene editing technology-single base editors.

Programmable nucleases are cutting edge genetic technology which edits targeted DNA sequences through generation of site-specific double-strand DNA breaks (DSBs). To improve the efficiency and precision of genetic modification, scientists have developed a single-base editing system (base editor) through combining of CRISPR/Cas9 system with cytosine deaminase. Compared with Cas9 system, this base editor can convert cytosine to thymine (C > T) at specific site more efficiently without inducing DSBs to avoid generation of indels. However, the base editor can only generate transition of pyrimidine but could not modify purines. Recently, Nature published a novel base editing system to convert adenine to guanine (ABEs, adenine base editors) through fusion of Cas9 nickase to a modified deaminase which is evolved through screening of random library based on tRNA adenine deaminase from E. coli. Here, we summarize the development of single-base editing tools and the latest research progress, especially the optimization process of ABEs, as well as the potential directions of the base editors.