prime editing

Prime editing works like the find-and-replace function in a text editor. You tell it where to look in the genome and exactly what the new text should be, and it writes that change in directly — without slicing both DNA strands and gambling on the cell's repair.

A prime editor joins a nickase Cas9 (which cuts only one DNA strand) to a reverse transcriptase, an enzyme that builds DNA from an RNA template. It is steered by a special prime editing guide RNA (pegRNA) that both targets the site and carries the desired edit written into its sequence. The reverse transcriptase copies that template directly into the genome, and the cell finishes the edit.

Prime editing is remarkably versatile: it can make all twelve possible single-base swaps plus small insertions and deletions, going beyond what base editors allow, all while avoiding full double-strand breaks. The trade-offs are that it is a larger, more complex machine, often less efficient, and harder to deliver into cells — so it complements rather than replaces simpler tools.