An emergency switch was found for the CRISPR system

Sofia Dolotovskaya, N+1

American scientists have found a way to turn off the CRISPR/Cas9 genome editing system using antagonist proteins found in the genome of bacteriophage viruses. This technology will improve the accuracy and safety of the CRISPR system. Article by Rauch et al. Inhibition of CRISPR-Cas9 with Bacteriophage Proteins is published in the journal Cell.

The CRISPR/Cas9 genome editing system, developed in 2012, allows targeted editing of an organism's DNA without affecting the rest of the genome. Cas9 endonucleases cut the DNA in the right areas, complementary to the "template" of the RNA guide, after which the cell's own repair systems stitch the ends of the DNA. Since, during repair, a cell usually uses an intact sample of homologous DNA from another chromosome, scientists can make changes to the genome by replacing this "standard" with any desired sequence.

The CRISPR/Cas9 system is based on a bacterial antiviral immunity system. Such immunity allows bacteria to find fragments of virus DNA in their CRISPR "file" (it is located in a certain part of the bacterial genome), and destroy viral DNA with the help of nuclease. Bacteria have several types of CRISPR system and several nucleases, but for the purposes of genome editing in bioengineering, Cas9 nuclease is most often used. In turn, bacteriophage viruses, from which bacteria are protected by such immune systems, produce proteins that block these systems. However, proteins blocking the CRISPR/Cas9 system have not been detected so far.

To search for such proteins, the authors of the new article focused on the analysis of profages – sections of the genome of the bacteriophage virus integrated into the genome of bacterial cells. The idea was that if a bacteriophage managed to embed its genes into the bacterial genome, bypassing the CRISPR/Cas9 protection system, it means that viruses have ways to block this system.

After analyzing about 30 strains of Listeria monocytogenes bacteria using the CRISPR/Cas9 system, scientists found genes of four types of proteins blocking this system in their prophages. Experiments using Escherichia coli cells and human cells have shown that two of these proteins, named AcrIIA2 and AcrIIA4, effectively blocked the bacterium's Cas9 nuclease Streptococcus pyogenes (it is most often used in bioengineering).

Drawing from an article in Cell – VM

The detected inhibitors will improve the accuracy of CRISPR/Cas9 by turning it on and off at the right time and regulating its activity in different parts of the genome or in different tissues. Also, the use of inhibitor proteins can make the CRISPR/Cas9 system safer: in the event that something goes wrong, its activity can be blocked.

CRISPR/Cas9 technology is being actively tested for the treatment of many genetic diseases. So, it was tested, for example, for the treatment of beta-thalassemia in human embryos, the removal of HIV genes from infected lymphocytes and the treatment of sickle cell anemia. In addition, scientists have recently developed a new CRISPR system that operates at the level of RNA, not DNA, and is able to specifically destroy the desired RNA using an RNA guide.

Portal "Eternal youth" http://vechnayamolodost.ru  09.01.2017