Base editors are precision tools for editing DNA that directly rewrite letters, or nucleotides, in the DNA sequence. There are two key differences of base editors to the traditional CRISPR-Cas9 system (sometimes referred to as DNA scissors). Firstly, in base editors, the Cas9 protein is modified not to cut both of the DNA strands. Secondly, by the addition of a new element, deaminase, base editors can carry out the converting, and thus rewriting, of nucleotides. There are two types of base editors: cytosine base editors (CBE) and adenine base editors (ABE). In CBE, the deaminase converts the cytosine to uracil (letter C to U), whereas the ABE first converts adenine to guanosine (letter A to G) by a two-step process where adenine is converted to an inosine and then to a guanosine.
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