In CRISPR-Cas9 genome editing, target specificity is determined by
- Acheck_circle
Base-pairing of the guide RNA (sgRNA) to a complementary DNA sequence adjacent to a PAM
- B
Methylation status of the host DNA at the cut site
- C
Cas9 protein recognizing a fixed 20-bp protein sequence motif
- D
Random binding of Cas9 to A/T-rich regions
Explanation
The sgRNA's spacer sequence pairs with target DNA; Cas9 also requires a PAM (e.g., NGG for SpCas9) immediately downstream. Changing the sgRNA spacer redirects Cas9 to a new target.