Search-and-replace genome editing — all 12 base changes, small indels, no DSB needed
Steps
Details
Prime Editor (PE2/PE3): nCas9 (H840A nickase) fused to an engineered MMLV reverse transcriptase.
The pegRNA (prime editing guide RNA) contains: spacer (targeting) + scaffold + primer binding site (PBS) + RT template. The PBS hybridizes to the 3' end of the nicked strand, priming reverse transcription of the new sequence.
Capabilities vs Others
Cas9: DSB → indels or HDR CBE: C→T only (transitions) ABE: A→G only (transitions) Prime editing: all 12 base changes + small indels + no DSB!
Efficiency: ~10-50% in cell lines. Ongoing work on PE4/PE5 (MLH1dn suppresses mismatch repair) and twin-PE for larger insertions.