Prime editing combines the best traits of CRISPR and base pair editing. Through modification of the Cas9 protein and addition of a “guide” RNA, the researchers have been able to target specific sequences and edit them with less than 10% chance of unwanted edits. The modified Cas9 snips a single strand of DNA rather then both strands of the double helix. Then, the guide RNA, pegRNA tethers to the site of the snip and encodes for the desired sequence. Then another Cas9 snips the opposite side of the first strand cut, creating damaged DNA. The cell then goes about its normal repair process with the help of reverse transcriptase. By allowing the cell to utilize its built-in process, the chances of unwanted edits are very small.
The research is currently conducted in vitro, however the results are astonishing. Since this method is much more precise then original CRISPR, many genetic disorders could be corrected. CRISPR is limited to small edits, where prime editing can edit larger sequences. I am looking forward to seeing what will be possible in the future through prime editing.
Link to article: https://singularityhub.com/2019/11/05/everything-you-need-to-know-about-superstar-crispr-prime-editing/