Step 1. The reverse transcriptase and Cas9 nickase enzymes form a complex with the prime editing guide RNA (pegRNA).

Step 2. The pegRNA’s guide sequence binds to the target DNA sequence.

Step 3. The Cas9 nickase enzyme cuts one strand of DNA.

Step 4. The pegRNA primer binding site then binds to the resulting DNA flap.

Step 5. The Reverse transcriptase enzyme adds DNA to the end of the flap using the RNA template located directly after the pegRNA’s primer binding site.

Step 6. The resulting DNA has one edited strand and one unedited strand.

Step 7. The cell’s DNA repair machinery resolves the conflict between the edited and unedited strands by picking one of them.

Back to the Prime Editing explainer blog post.