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CRISPR applications in nature. Illustration by Linnea  Holmström Ljung

What is CRISPR-Cas9?

CRISPR-Cas9 is a new technology that makes genetic manipulation fast and simple. The CRISPR-Cas9 system was originally discovered as a bacterial defense mechanism against foreign DNA introduced by bacteriophages. The technology is already widely used both as a tool in research laboratories and to develop novel therapeutics for serious diseases. 

CRISPR-Cas9 is a precise gene-editing tool that can correct defective DNA, much like a text editing software can edit or correct typos in your document. It functions as a target-seeking molecular scissors, kind of like a Swiss army knife that can be used to introduce a variety of changes into the genome of any cell or organism.


The tool is an RNA programmable enzyme that functions as scissors to cleave DNA and that can easily be designed for targeting any gene in a cell in order to modify it. It is henceforth possible to modify gene expression, to switch it “on” or “off,” to change, repair or remove genes.


The RNA consists of a single RNA that can be programed to guide the enemy to modify the sequence of DNA of interest in the genomes of any cell and organism.


What does CRISPR-Cas9 stand for?


CRISPR refers to Clustered Interspaced Short Palindromic Repeats occurring in the genome of certain bacteria, in which the system was discovered.


Cas-9 stands for CRISPR-associated endonuclease number 9 and was previously known as Csn1 or Cas5.


We found this system in Streptococcus pyogenes which is a flesh eating bacteria.


Bacteria have an adaptive immune system, which allows them to defend themselves against predators. This can be the viruses of bacteria called bacteriophages. The adaptive immune system is composed of an RNA component that carries the memorisation of a previously encountered virus, for example, and  some proteins that will allow the memorization event and also subsequently prevents the attack or the predators from a second infection.


Focussing on one such RNA, which is now known as the tracrRNA we ended up asking the question whether the RNA would interfere with the adaptive immune system of the bacteria called CRISPR Cas. Indeed we found that this RNA can form a duplex with a CRISPR RNA component, which is a memory device of this adaptive immune system and can guide a protein of the system that has the function to cleave the DNA of invading viruses.


The mechanism that we discovered is that the two RNA molecules interfere with one another to form a single duplex RNA that guides an endonuclease, a protein that has the possibility to cleave DNA, to the target virus DNA. When we followed up on the pathway of this adaptive immune system it became clear that this system would carry a high potential as a new molecular biology tool.


The mechanisms of DNA targeting called CRISPR-Cas9 is unique in nature and has very quickly been adopted by the scientific community as a new tool to manipulate DNA. By adjusting the sequence of the RNA signature of CRISPR-Cas9, the complex can be targeted to cleave or modify a genome in a sequence-specific manner. The system is considered as a game-changer and is on the way to revolutionize the genetics of cells and model organisms in the lab.

Today thousands of laboratories use CRISPR-Cas9 in their research.

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