CRISPR-Cas9–mediated GGCX knockout in HEK293 reporter cells. (A) Six optimized gRNA sequences for GGCX targeting and a nontargeting gRNA sequence as the control. (B) Carboxylation activity of HEK293 reporter cells targeted by different gRNAs, as shown in panel A. (C) Insertion and deletion mutations (indels) introduced by Cas9-gRNA-5 in the target site. The wild-type sequence is shown at the top. Dashes, deletions; italic lowercase letters, insertions. The sizes of indels are indicated to the right of each sequence.