Fig. 1.

Base editing of genomic DNA in human cells by sgCBE. a Cartoon representation of the Cryo-EM structure of SpyCas9 in complex with DNA and sgRNA. Loops of SpyCas9 sgRNA for inserting MS2 tag were shown in red spheres. b Sequence of SpCas9 and schematic diagram of MS2-modified sgRNA scaffold. c Organization of sgRNA-derived cytosine base editor (sgCBE). SpyCas9 D10A nickase, APOBEC1, and MS2-sgRNA were expressed separately. The cytosine deaminase, APOBEC1, was fused with MCP and UGI in its N-terminus and C-terminus, respectively, to form MCP-APOBEC1. d Efficiency of cytosine editing with various MS2-sgRNA-derived base editors. HEK293T cells were transfected with plasmids harboring SpCas9 nickase, MCP-APOBEC1, and different MS2-modified sgRNA to form sgCBE. Target Cs were shown in red, with a subscripted number denoting their relative position to PAM (counting NGG PAM as + 21 to + 23), and the PAM sequence was shown in blue. C-to-T editing efficiencies were analyzed by Sanger sequencing and EditR calculating. Each experiment was repeated at least three times. Data are represented as mean ± SEM; ^nsp > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001