Base editing with a Cpf1-cytidine deaminase fusion.

The targeting range of CRISPR-Cas9 base editors (BEs) is limited by their G/C-rich protospacer-adjacent motif (PAM) sequences. To overcome this limitation, we developed a CRISPR-Cpf1-based BE by fusing the rat cytosine deaminase APOBEC1 to a catalytically inactive version of Lachnospiraceae bacterium Cpf1. The base editor recognizes a T-rich PAM sequence and catalyzes C-to-T conversion in human cells, while inducing low levels of indels, non-C-to-T substitutions and off-target editing.