How does CRISPR work?

The CRISPR-Cas9 System

CRISPR is a gene editing system identified in bacteria where it is used as a defence against viral attack.

How CRISPR works

Identified in archaea and bacteria, short nucleic acid sequences are captured from invading pathogens and integrated in the CRISPR loci amidst the repeats.

Small RNAs, produced by transcription of these loci, can then guide a set of endonucleases to cleave the genomes of future invading pathogens, thereby disabling their attacks.

Using CRISPR in the lab

Scientists can leverage the CRISPR mechanism using a guide RNA (gRNA) for targeting and Enodnuclease (Cas9), often referred to as ‘Molecular Scissors’, to effect a double-strand break in the cell DNA at a targeted location, enabling knockout or knockin of gene function.

What is Cas9?

Definition: Cas9 is a protein (bacterial nuclease) that can be programmed by a small guide RNA to cleave DNA at almost any given genomic locus.

Following this cleavage event, the DNA is repaired, mostly by non-homologous end joining. The DNA repair mechanism is imprecise, therefore it frequently creates small insertions or deletions, often leading to frameshift mutations.

Cas9 was the first of several restriction nucleases (or molecular scissors) discovered that enable CRISPR genome editing. The CRISPR Cas9 mechanism has since been adapted into a powerful tool that puts genome editing into the mainstream.

For more information on CRISPR gene editing watch our introductory webinar

A guide to CRISPR genome editing

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