[Prime-Editing Methods and pegRNA Design Programs]

It has been 10 years since CRISPR/Cas technology was applied to edit the genomes of various organisms. Its ability to produce a double-strand break in a DNA region specified by the researcher started a revolution in bioengineering. Later, the Base Editing (BE) method was developed. BE is performed via the formation of single-strand breaks by the mutant form of Cas nuclease (nickase), fused with deaminases and other enzymes. It can be used to promote A ↔ G and C ↔ T transitions, and a C → G transversion. Just over 3 years ago, a new Prime Editing (PE) variant of CRISPR/Cas was invented. Unlike BE, in PE the nickase is fused with reverse transcriptase, capable of building a new DNA chain using the pegRNA template. The pegRNA consists of an elongated guide RNA with an extra sequence at the 3'-end. Prime editing makes it possible to insert the desired mutations into this extra sequence and to carry out any substitutions and indels of bases without the use of special donor DNA. To date, a number of PE variants have been proposed; they are briefly considered in this review with an emphasis on prime editing of plant genomes. Some attention is also paid to pegRNA design programs, as well as evaluation of the efficiency of the editing. Such a variety of PE techniques is due to the opportunities of high-precision introduction of desired changes with a rather low frequency of off-target mutations in the genomes of various organisms. The relatively low efficiency of prime editing inspires researchers to offer new approaches. There is hope that further development of the technology will improve PE enough to take its rightful place among the genome targeting methods that are suitable for any organisms, and will have a positive impact on the agricultural sector, industrial biotechnologies, and medicine.