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Scientists Find Cas9 Enzyme That Targets HCV in Human Cells

NEW YORK (GenomeWeb) – Scientists this week described a new mechanism by which Cas9 proteins can target viral RNA.

In a paper published in the Proceedings of the National Academy of Sciences, the researchers from Emory University detailed the use of a Cas9 variant from the gram-negative bacterium Francisella novicida that can inhibit viral protein production from hepatitis C virus (HCV) RNA.

"This work demonstrates a portable, interdomain machinery capable of viral inhibition, likely just one of myriad potential biotechnological and medical applications of Cas9-mediated RNA targeting," the authors wrote.

The researchers designed an RNA-targeting guide RNA (rgRNA) for use with F. novicida Cas9 (FnCas9) to target HCV, which never has DNA in its life cycle. They were able to prove that FnCas9 could inhibit gene expression in human hepatocellular carcinoma cells, but they didn't know exactly how it worked.

To find out, they used point mutations in different domains of the FnCas9 gene and were able to identify the RNA-binding arginine-rich motif as one that diminished the ability of FnCas9 to inhibit HCV gene expression. The authors also showed that even a catalytically inactive FnCas9 was able to inhibit both translation and replication of HCV RNA.

Moreover, the FnCas9 enzyme was able to inhibit the virus in an established infection, indicating a unique potential for the FnCas9-rgRNA complex. The authors noted that both RNA and DNA viruses require an RNA stage at some point, adding that FnCas9 could target both negative- and positive-sense RNA strands.

"The FnCas9:rgRNA machinery could facilitate the targeting of viruses as soon as their genome sequences are available, without knowledge of the virus life cycle or host receptors," they wrote.

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