In nature, bacteria use CRISPR-Cas9 to defend against viral infection (bacteriophages). When a bacterium survives a viral attack, it integrates a short fragment of the viral DNA into its own genome at the CRISPR locus. This locus then transcribes CRISPR RNA (crRNA) that guides the Cas9 nuclease to recognize and cleave any matching viral DNA upon reinfection.
The cell repairs the DSB through two competing mechanisms:
Cas9 can tolerate mismatches between the sgRNA and DNA, especially in the PAM-distal region. This risks unintended mutations in functional genes, potentially causing oncogene activation. Engineered high-fidelity variants (eSpCas9, SpCas9-HF1) reduce off-target activity by >90% while retaining on-target efficiency.
HDR is limited to dividing cells and is inefficient in most primary human cells (e.g., neurons, cardiomyocytes). New methods like prime editing (Cas9 nickase fused to reverse transcriptase) and base editing (deaminase-Cas9 fusion) bypass DSBs entirely.
In nature, bacteria use CRISPR-Cas9 to defend against viral infection (bacteriophages). When a bacterium survives a viral attack, it integrates a short fragment of the viral DNA into its own genome at the CRISPR locus. This locus then transcribes CRISPR RNA (crRNA) that guides the Cas9 nuclease to recognize and cleave any matching viral DNA upon reinfection.
The cell repairs the DSB through two competing mechanisms: completely science
Cas9 can tolerate mismatches between the sgRNA and DNA, especially in the PAM-distal region. This risks unintended mutations in functional genes, potentially causing oncogene activation. Engineered high-fidelity variants (eSpCas9, SpCas9-HF1) reduce off-target activity by >90% while retaining on-target efficiency. In nature, bacteria use CRISPR-Cas9 to defend against
HDR is limited to dividing cells and is inefficient in most primary human cells (e.g., neurons, cardiomyocytes). New methods like prime editing (Cas9 nickase fused to reverse transcriptase) and base editing (deaminase-Cas9 fusion) bypass DSBs entirely. The cell repairs the DSB through two competing