CRISPR-Cas12 and CRISPR-Cas13 in the diagnosis of infectious diseases (Part 5)
Welcome to the 5th part of the 12-part series on CRISPR-Cas system based diagnosis of COVID-19.
After establishing the importance of the CRISPR-Cas9 system in gene editing, scientists are harnessing this technology for diagnosing infectious diseases. A team of scientists found that Type V Cas12 and Type VI Cas13 enzymes can be harnessed to detect human disease.
While Cas12 targets DNA, Cas13 targets the RNA. Part of the mechanism of their action is similar to that of Cas9. A guide RNA that is complementary to the target sequence is required for the specific binding of Cas enzymes, and then the Cas12 or Cas13 proteins cleave at the target site. An additional exciting feature of Cas12 and Cas13 enzymes is that they show trans or collateral cutting activity (Fig 1). It means that on finding the target, the cleavage activity of Cas12 and Cas13 enzymes is not just restricted to the target DNA or RNA; they can also cut any single-stranded non-targeted nucleic acid molecules in the vicinity.
Although this collateral DNase and RNase activity might appear to be a disadvantage in terms of specific gene editing, it has made these enzymes a powerful tool for developing CRISPR-based diagnostics. The collateral cutting activity of these enzymes has attracted scientists to build reporter systems in CRISPR diagnostics (Parts 6, 7, and 8).
Even before the coronavirus pandemic, researchers and companies had already made considerable progress on this front, but when the COVID-19 crisis began to take hold across the world, two US start-ups Sherlock Biosciences and Mammoth Biosciences, acted quickly to take the initiative in developing the CRISPR based diagnostic kits for COVID-19.
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