Utilizing an unsuspected activity of the CRISPR-Cas12a protein,  researchers created a simple diagnostic system called DETECTR to analyze cells, blood, saliva, urine and stool to detect genetic mutations, cancer and antibiotic resistance and also diagnose bacterial and viral infections. The scientists discovered that when Cas12a binds its double-stranded DNA target, it indiscriminately chews up all single-stranded DNA. They then created reporter molecules attached to single-stranded DNA to signal when Cas12a finds its target. CRISPR-Cas12a, one of the DNA-cutting proteins revolutionizing biology today, has an unexpected side effect that makes it an ideal enzyme for simple, rapid and accurate disease diagnostics. Cas12a, discovered in 2015 and originally called Cpf1, is like the well-known Cas9 protein that UC Berkeley's Jennifer Doudna and colleague Emmanuelle Charpentier turned into a powerful gene-editing tool in 2012. CRISPR-Cas9 has supercharged biological research in a mere six years, speeding up exploration of the causes of disease and sparking many potential new therapies.

Cas12a was a major addition to the gene-cutting toolbox, able to cut double-stranded DNA at places that Cas9 can't, and, because it leaves ragged edges, perhaps easier to use when inserting a new gene at the DNA cut. But co-first authors Janice Chen, Enbo Ma and Lucas Harrington in Doudna's lab discovered that when Cas12a binds and cuts a targeted double-stranded DNA sequence, it unexpectedly unleashes indiscriminate cutting of all single-stranded DNA in a test tube. This protein works as a robust tool to detect DNA from a variety of sources. We want to push the limits of the technology, which is potentially applicable in any point-of-care diagnostic situation where there is a DNA component, including cancer and infectious disease. The chance discovery of Cas12a's unusual behavior highlights the importance of basic research, since it came from a basic curiosity about the mechanism Cas12a uses to cleave double-stranded DNA. It's cool that, by going after the question of the cleavage mechanism of this protein, we uncovered what we think is a very powerful technology useful in an array of applications. Additional co-authors of the paper are undergraduate Xinran Tian of UC Berkeley and Maria Da Costa and Joel Palefsky of UCSF. The work was supported primarily by the National Science Foundation.

Regards
ALEX JOHN
Editorial Assistant
Journal of infectious disease and dignosis