Cutting Once Is Harder Than It Sounds: Your Guide to Minimizing Off-Target Effects

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A protein structure of ABE8e is shown, superimposed with cartoon representations of sgRNA and target DNA. Two TadA domains are highlighted. The catalytic domain contacts multiple bases of the non-target DNA strand, while the docking domain primarily contacts the other protein domains.
A cartoon showing a simplified Cas9 and gRNA binding to DNA. The 3’ end of the gRNA is the scaffold sequence, bound by Cas9, where some DNA substitution is tolerated. The 20 bases on the 5’ end of the gRNA are the spacer sequence, which hybridizes with the genomic DNA, base pairing to the target strand.   The non-target strand of genomic DNA includes the same sequence as the spacer. The PAM consists of the three bases immediately 3’ of this spacer-matching sequence.  Within the gRNA spacer, the 3’ half is the seed sequence, where no DNA substitution is tolerated. The 5’ half, also the 5’ end of the entire gRNA, is the tail sequence, where DNA substitution is tolerated.
A smiling Blugene holds DNA
Cartoon of CRISPR-associated transposase (CAST) integrating donor DNA into a genomic target site.
A schematic overview of the CRISPR classification system.
A cartoon depiction of cytidine base editing. A base editor, consisting of a cytidine deaminase fused to Cas9, is shown binding to DNA using its guide RNA. The guide RNA base pairs to target DNA, leaving the opposite strand of DNA free to be contacted by the cytidine deaminase, which converts a C to a U within this single-stranded sequence. This deamination yields DNA with a G:U mismatch without creating a double-strand break. Mismatch repair preserves the edit IF the modified strand is used as the template, converting the mismatched G to an A and yielding a single-base-pair edit.
Diagram of the Cascade complex with gRNA bound to target DNA, after recruitment of Cas3. Cas3 is about to nick the non-target strand.

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