By Meghan Bialt-DeCelie ’19

Since the explosion of CRISPR-Cas 9, a gene editing technology, researchers have been further exploring its mechanisms and ways of improving the system. AcrIIA4 is a known anti-CRISPR protein that inhibits the CRISPR-Cas 9 complex, but the mechanism and residues involved were not as explored.

Researchers lead by Jiyung Shin, PhD from The University of California Berkley investigated AcrIIA4 to understand its structure and function in inhibiting the Cas 9 complex. They found that the anti-CRISPR doesn’t directly bind to the Cas 9 complex, but rather it mimics DNA targets to bait the Cas 9 complex with the single-guide RNA. The researchers exposed linearized plasmid DNA to the Cas 9 complex and AcrIIA4 simultaneously, with a 6-hour delay in between and in reverse order (AcrIIA4 then Cas 9). Results showed that AcrIIA4 effectively turned off gene editing. This revealed the importance of the order and timing of adding these gene editing tools for getting the desired product. The use of AcrIIA4 improved CRISPR gene editing by giving scientists better control of Cas 9 with cutting desired targets.

With this understanding of the anti-CRISPR, researchers saw AcrIIA4 as an “off switch” which can allow gene editing to be more specific and precise, as it would prevent off target binding.

References:

1. J. Shing, et al, Disabling Cas9 by an anti-CRISPR DNA mimic. Science 3, 1-9 (2017). doi: 10.1126/sciadv.1701620
2. Image retrieved from: https://de.wikipedia.org/wiki/Cas9