Prime Editing Tool - An emerging advancement in the gene editing

The best-known gene-editing technology so-far is CRISPR-Cas, but new players are entering the field with more features and improvements. Prime Editing, a new tool which is still in its development, but its uses are far-reaching. Below, we'll take a fast look at the new editing tool and followed by a brief summarisation.

Prime Editing Tool

The best-known gene-editing technology so-far is CRISPR-Cas, but new players are entering the field with more features and improvements. Prime Editing, a new tool which is still in its development, but its uses are far-reaching. Below, we'll take a fast look at the new editing tool and followed by a brief summarisation.

What is prime editing?

The first thing to note is that Prime Editing is a lab-developed gene editing tool, a relatively new technology that was introduced in late 2019. Because it is a targeted gene-editing technology, it can target specific DNA sites to replace genetic information. Therefore, insertions, deletions, and transformations can be facilitated without cutting both DNA strands or using a DNA template.

Components of prime editing tool

Prime Editing consists of three main components. Prime Editing Guide RNA (pegRNA) identifies a sequence of bases to be edited and encodes a new sequence to replace the target. The pegRNA consists of an extended single guide RNA (sgRNA) with a primer binding site (PBS) and a reverse transcriptase template sequence.

The Fusion protein made up of two enzymes:

  1. The first enzyme is the Cas9 H840A nickase (“Nickase”), which specifically cleaves single strands.The Cas9 enzyme portion of the nickase has a substitution in it to cause a single-strand break, rather than a double-stranded cut.
  2. The second enzyme is an M-MLV (Moloney murine leukemia virus) reverse transcriptase ,which synthesizes DNA from a single-stranded RNA template.

How prime editing tool works?

  1. Prime editing works by delivering pegRNA and fusion proteins to target cells. Once inside the cell, the fusion protein cleaves the cell's DNA at the target sequence and initiates reverse transcription of the template sequence found in the pegRNA. This creates an edited DNA strand and an unedited DNA strand. First, the untreated strand is removed, then the newly treated strand recombines to form double-stranded DNA.
  2. This then creates a mismatch in the base pairs between the two strands, which can have two outcomes. In one outcome, using the mismatch repair mechanism of the cell, the edited strand is copied to the complementary strand, which incorporates the edited strand into the DNA of the cell. Conversely, the original base sequence is reincorporated into the edited strand from the complementary strand, removing the edit from the DNA of the cell.

Advantages and disadvantages of the tool

Advantage of prime editing tool

  1. Prime editing is a highly precise and can be used flexibly along the DNA genome due to the single-stranded pegRNA, which allows for all types of insertions into the gene sequence, such as substituting or transitioning bases.
  2. The prime editing uses the cells’ intrinsic DNA mismatch system to incorporate changes in the nucleotide order into the cell, this reduces the number of unwanted or random by-products of genome editing.  There are potentially fewer off-target effects than with the CRISPR-Cas9 system; potentially marking it as a future technology for human therapeutic uses.

Disadvantage of prime editing tool

Undeniably, the main disadvantage to prime editing is its relatively new – it came to the forefront in late 2019. It is still at proof-of-concept stage, with no therapeutic uses as of yet.