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Enhanced proofreading governs CRISPR-Cas9 targeting accuracy.

Janice S Chen1, Yavuz S Dagdas2, Benjamin P Kleinstiver3,4,5

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New CRISPR-Cas9 variants (SpCas9-HF1 and eSpCas9(1.1)) show reduced off-target effects. A novel hyper-accurate variant (HypaCas9) was developed, improving genome editing specificity without losing on-target activity.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • The CRISPR-Cas9 system from Streptococcus pyogenes (SpCas9) is a powerful tool for genome editing.
  • Existing high-fidelity variants (SpCas9-HF1, eSpCas9(1.1)) reduce off-target cleavage but their target discrimination mechanisms remain unclear.
  • Further improvements in Cas9 specificity are needed for precise genome engineering.

Purpose of the Study:

  • To elucidate the mechanism underlying target discrimination in SpCas9 variants.
  • To engineer a novel Cas9 variant with enhanced specificity and maintained on-target activity.
  • To develop a refined model for Cas9 target recognition and nuclease activation.

Main Methods:

  • Single-molecule Förster resonance energy transfer (smFRET) experiments were employed to study SpCas9 variants.
  • Biophysical techniques were used to analyze target binding and conformational changes.
  • A new Cas9 variant, HypaCas9, was designed and tested for genome-wide specificity and on-target activity.

Main Results:

  • SpCas9-HF1 and eSpCas9(1.1) adopt inactive states when binding mismatched DNA targets.
  • The REC3 domain of Cas9 plays a critical role in recognizing target complementarity and controlling nuclease activity.
  • The newly designed HypaCas9 variant exhibits superior genome-wide specificity and robust on-target editing in human cells.

Conclusions:

  • The REC3 domain is a key regulator of Cas9 catalytic competence based on target DNA matching.
  • Understanding this mechanism allows for the rational design of more accurate CRISPR-Cas9 tools.
  • HypaCas9 represents a significant advancement in precision genome editing technologies.