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The prime editing machinery comprises a prime editing guide RNA (pegRNA) and a Cas9 nickase enzyme fused to a reverse transcriptase.

          The prime editing machinery comprises a prime editing guide RNA (pegRNA) and a Cas9 nickase enzyme fused to a reverse transcriptase.
          (Left) The pegRNA binds to a matching sequence on the target DNA strand.(Right) The Cas9 nickase cuts the unbound complementary strand, creating a flap.
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The pegRNA binds to a matching sequence on the target DNA strand.

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The Cas9 nickase cuts the unbound complementary strand, creating a flap.

         
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The dangling DNA flap binds to a matching sequence on the other end of the pegRNA.

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The reverse transcriptase extends the flap by filling in the desired insertion sequence from the template next to the binding site.


          The edited flap competes with and displaces the flanking nucleotide sequence (right), which is ultimately removed by the cell. The opposite strand is nicked and repaired to match the newly edited flap, completing the edit.
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The edited flap competes with and displaces the flanking nucleotide sequence (right), which is ultimately removed by the cell.

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The opposite strand is nicked and repaired to match the newly edited flap, completing the edit.

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Reference

  1. Anzalone AV, et al. Search-and-replace genome editing without double-strand breaks or donor DNA. Nature. 2019;576(7785):149-157.

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