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There’s a new CRISPR enzyme for editing

This just-described Cas variant may eventually be used in both diagnostics and therapeutics
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A new, more compact CRISPR-Cas enzyme has been found in the genomes of huge bacteriophages.

The discovery, announced in Science by a team of researchers from the United States and Australia, included a minimally functional CRISPR-Cas system dubbed Casφ, is composed of a single 70-kilodalton protein and a CRISPR array in the bacteriophage genome.

“Casφ uses a single active site for both CRISPR RNA (crRNA) processing and a crRNA-guided DNA nuclease to target foreign nucleic acids,” the authors stated.

This tool, they said, can be used for genome editing and DNA detection but at half the molecular weight of Cas9 and Cas12a genome editing enzymes. It can target a wider range of genetic sequences than Cas9 and Cas12, noted a news release. Its target-expanding abilities were tested on both human and plant cells.

Smaller Cas enzymes are good because they simplify the delivery of CRISPR-Cas systems into cells, and this new system may eventually be used in both diagnostics and therapeutics. Smaller sizes also help vector-based cell deliveries and potentially a wider range of targetable genomic sequences.

“Useful for genome editing and DNA detection but with a molecular weight half that of Cas9 and Cas12a genome-editing enzymes, Casφ offers advantages for cellular delivery that expand the genome editing toolbox,” the authors wrote in the paper’s abstract.

The Casφ nuclease was first described this winter in a paper published in Nature as part of a DNA sequence from diverse ecosystems. That study uncovered hundreds of phage genomes which were more than 200 kilobases long—including one that was 735 kilobases.

“Almost all phage CRISPR systems lack spacer acquisition machinery (Cas1, Cas2 and Cas4) and many lack recognizable genes for interference,” the authors of the Nature study wrote.

This is likely the tip of the Cas iceberg, study o-author Basem Al-Shayeb, from the University of California, Berkeley, told Genome Web.

"Even with all our knowledge on bacteria and viruses so far, we are barely scratching the surface regarding what is out there," he said. "We are able to cultivate below 1 percent of the bacteria we know, and a small fraction of the viruses that infect that 1 percent. There is a lot to learn about the biology around us and what these entities can do."

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