A team of researchers has solved a potential problem with the CRISPR-Cas9 gene editing method by discovering a way to shut it off. The team’s method, which utilizes bacteriophage proteins, allows for more precise gene editing and gives researchers the ability to deactivate the entire system if necessary. The details are in a paper that was just published in the journal Cell.
CRISPR-Cas9 is a method that scientists use to edit genomes. Cas9 is an enzyme that snips off pieces of DNA so they can be replaced. The CRISPR-Cas9 system is naturally found in bacteria as a way to combat bacteriophages, viruses that only target bacteria. Sections of viral DNA are cut and stored so that the bacterium can recognize the bacteriophage in the future. Researchers take advantage of this system to modify genomes and fix genetic disorders. However, CRISPR-Cas9 occasionally makes mistakes. In the past, scientists didn’t have a way to deactivate the system, leading to questions of safety in future human trials.
Researchers from the University of California, San Francisco investigated possible methods of deactivating the CRISPR-Cas9 system. CRISPR-Cas9 is primarily a way for bacteria to fight viruses but the team observed bacteria that had still been infected. If a bacteriophage infected the bacterium and inserted its DNA, Cas9 should try to cut it out—even though it would be targeting the bacterium’s own genome. This would be bad for the virus since it needs to have a living host. The research team speculated that some bacteriophages had anti-CRISPR proteins that were used to deactivate Cas9. After screening for bacteria that had been infected this way, the team found two anti-CRISPR proteins called AcrIIA2 and AcrIIA4. Both proteins were capable of inhibiting the Cas9 enzyme. AcrIIA2 and AcrIIA4 could be used to deactivate Cas9, switching off the entire CRISPR-Cas9 system.
The team’s findings will give scientists better control over gene editing. If the CRISPR-Cas9 system begins to make mistakes, researchers can deactivate it. The system can be turned off temporarily or permanently. This will make the technique safer to use in eventual human trials.
Rauch et al. Inhibition of CRISPR-Cas9 with Bacteriophage Proteins. Cell (2016).