Researchers Discover Off-Switch to CRISPR-Cas9 Gene Editing System

Researchers from the University of California, San Francisco have found a way to switch off the CRISPR-Cas9 gene editing system using newly identified anti-CRISPR proteins that are produced by bacterial viruses. The newly discovered anti-CRISPR proteins could enable more precise control in CRISPR applications, but also provide a fail-safe to quickly block any potentially harmful uses of the technology.

To find an anti-CRISPR protein that would work against the CRISPR-Cas9 system used in most labs which depends on a protein called SpyCas9 as its targeted DNA clippers, the researchers thought that they should be able to identify bacteria with inactivated CRISPR systems. This can be conducted by looking for evidence of so-called "self-targeting" – bacterial strains where some virus had successfully gotten through the Cas9 blockade and inserted its genes into the bacterial genome.

The research team examined nearly 300 strains of Listeria, and found that 3 percent of strains exhibited "self-targeting." Further investigation isolated four distinct anti-CRISPR proteins that proved capable of blocking the activity of the Listeria Cas9 protein, which is very similar to SpyCas9.

Further research showed that two of the four anti-CRISPR proteins, called AcrIIA2 and AcrIIA4 by the researchers, worked to inhibit the ability of the commonly used SpyCas9 to target specific genes in other bacteria, as well as in engineered human cells. Together, the results suggest that AcrIIA proteins are potent inhibitors of the CRISPR-Cas9 gene editing system as it has been adopted in labs around the world.

For more details, read the news release from UC San Francisco.