CRISPR-Cas9

CRISPR-Cas9 is a genome editing tool that is revolutionary in the scientific world. It is faster, cheaper and more accurate than previous techniques of editing DNA and has a wide range of potential applications.

It is a unique technology that enables genetic scientists to edit parts of the genome by removing, adding or altering sections of the DNA base sequence. CRISPR is currently the simplest and most precise method of genetic manipulation in the scientific community.

The CRISPR-Cas9 system consists of two key molecules that are able to alter DNA. These are:

•  an enzyme called Cas9- which acts as a pair of ‘molecular scissors’ that can cut the two strands of DNA at a specific location in the genome so that DNA can be added or removed (the generic type of molecule is called a restriction enzyme).
•  a piece of RNA called guide RNA (gRNA), which consists of a small piece of pre-designed RNA sequence (about 20 bases long) located within a longer RNA scaffold. The scaffold binds to DNA and the pre-designed sequence ‘guides’ Cas9 to the right part of the genome, ensuring the right DNA sequence is changed.

The guide RNA is designed to find and bind to a specific sequence in the DNA. The guide RNA has RNA bases that are complementary to those of the target DNA sequence. This means that, in theory, the guide RNA will only bind to the target sequence and no other regions of the genome, meaning that only the preferred section of DNA is altered.
The Cas9 follows the guide RNA to the relevant location in the sequence and cuts across both strands of the DNA. At this stage the cell recognises that the DNA is damaged and tries to repair it. It can theoretically change both alleles of a gene.