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By making a small change to the sequence of the Cas9 protein researchers can control the enzyme\u2019s activity. Credit: B. L. Oakes\u00a0et al.<\/i>\/Cell<\/i><\/p>\n
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A bacterial enzyme that researchers often use to modify other organisms\u2019 genomes can also be harnessed to tackle invaders.<\/p>\n
The Cas9 enzyme naturally cuts DNA at targeted sites, guided by short \u2018CRISPR\u2019 sequences. David Savage at the University of California, Berkeley, and his colleagues added a trigger that allows proteases \u2014 enzymes that chew up proteins \u2014 to activate Cas9.<\/p>\n
The team used a linker to join the two ends of the Cas9 protein together in such a way that the protein\u2019s activity was locked. The resulting enzyme couldn\u2019t function unless a protease cleaved the linker.<\/p>\n
The researchers inserted the circularized Cas9 into cultured human cells and expressed a protease made by flaviviruses, a genus that includes the Zika and dengue viruses. The protease activated the Cas9 enzyme, which the researchers had programmed to cut a specific repetitive DNA sequence in the genome, causing the cells to die. The approach could be used to create other Cas9 variants, the authors say.<\/p>\n
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