Gene editing is a precise modification of the genome, which is an important means of studying gene function. At present, the commonly used gene editing method is the CRISPR-Cas9 system. After a decade of development, the CRISPR-Cas9 system has made breakthroughs in gRNA, PAM, single base editing, and multi bases editing. However, it is still difficult to achieve arbitrary modification of bases.
In 2019, Professor David Liu's team from Harvard University developed a method for precise gene editing based on CRISPR - Prime editing. In theory, Prime editing can achieve the editing effects of all editing methods today.

Prime editing is a technology optimized on the basis of traditional CRISPR/Cas9. Prime editing consists of two parts: one is nCas9 and reverse transcriptase fusion protein, and the other is pegRNA (prime editing gRNA). Unlike general gRNAs, pegRNA not only targets to specific DNA region that needs to be edited, but also carrying a "reverse transcription template".

Cas9-reverse transcriptase fusion protein will precisely cleave the target DNA single strand under the guidance of pegRNA, and then synthesize DNA containing the corrected bases according to the "reverse transcription template". The DNA repair mechanism within cells will integrate this newly synthesized sequence into the genome.