CRISPR

The first CRISPR – or clustered regularly interspaced short palindromic repeats – system to be used for gene editing was CRISPR/Cas9. There are now a number of different CRISPR systems used for gene editing purposes, with researchers continually developing new and improved systems for a multitude of different applications.

CRISPR/Cas9 is the most often used CRISPR gene editing system. When CRISPR/Cas9 is added to a cell along with a guide RNA (gRNA) molecule, the Cas9 enzyme binds to the gRNA, which is about 20 bases long and designed to be complementary to the target sequence within the DNA to be edited. The gRNA will also bind to the complementary region of DNA, and Cas9 will then cut the DNA at the desired target. The cell then recognizes that the DNA is damaged and tries to repair it.

During this repair process, alterations to the DNA sequence are introduced. In the case of Cas9, these mutations often disable a gene. Other enzymes can also be used that lead to different outcomes, including Cas12a. CRISPRi and CRISPRa use customized Cas proteins that do not cut or alter DNA but can turn genes on or off.