# Prime Editing in Dividing and Quiescent Cells

## TL;DR

This paper explores why prime editing works better in dividing cells and how to improve it in non-dividing cells.

## Contribution

The paper identifies SAMHD1 as a key factor limiting prime editing efficiency in quiescent cells and suggests ways to mitigate its effects.

## Key findings

- Prime editing efficiency is higher in dividing cells due to high dNTP levels and active DNA repair enzymes.
- SAMHD1 reduces prime editing efficiency in non-dividing cells by lowering dNTP levels.
- Inhibiting SAMHD1 improves prime editing outcomes in quiescent cells.

## Abstract

Prime editing is a method of genome editing based on reverse transcription. Recent results have shown its elevated efficiency in dividing cells, which raises some questions regarding the mechanism of this effect, because prime editing does not employ homology-driven repair. This mini review aims to identify the reason for this phenomenon and find a possible solution to the problems that it poses. In dividing cells, prime editing takes advantage of high levels of dNTPs and active endonuclease and ligase machinery, such as FEN1 endonuclease and LIG1 ligase, but DNA mismatch repair, which is closely associated with replication, works against prime editing. Prime editing is a method which relies on retroviral reverse transcription, so mechanisms of intrinsic anti-retroviral defense should also work against editing. One of the factors which drastically reduce the efficiency of reverse translation is SAMHD1, which maintains low levels of dNTPs in non-dividing cells. Recent works aimed at the mitigation of SAMHD1 function demonstrated a significant increase in prime editing efficiency.