How it Works

CRISPR, which stands for “clustered regularly interspaced short palindromic repeats,” is a DNA sequence found in bacteria. The discovery of CRISPR dates back to the 1980s, when researchers at Osaka University sequenced the genomes of common bacteria. They found the repeating DNA sequences in many species but did not know its biological purpose.

Years later, scientists in the dairy industry confirmed that bacteria use CRISPR to destroy viruses. The molecular system works by incorporating “spacer” DNA sequences that match the DNA of viruses that have previously attacked the bacteria and its ancestors. When a virus attacks, RNA made from the CRISPR DNA binds to the matching viral DNA by Watson-Crick base-pairing. The RNA also binds to a DNA-cutting protein called a nuclease, and the formation of the whole complex results in the viral DNA being chopped up and destroyed. If an unknown virus attacks, the CRISPR system makes new spacer sequences to protect it against the virus in the future.

With this knowledge in hand, the dairy industry identified different strains of bacteria and could see whether bacterial cultures used in products such as yogurt or cheese were immune to specific viruses.
It wasn’t until 2012, however, that researchers discovered a way to leverage the CRISPR system to slice up any DNA sequence in bacteria, viral or not. The type of CRISPR system they used involved a nuclease called Cas9. The researchers could engineer the CRISPR DNA sequence to make an RNA that matched essentially any DNA target they wanted. The RNA bound to Cas9 would do the rest, finding the matching DNA sequence and cutting it.
Since then, researchers across the globe have worked at an incredible pace to use CRISPR for further applications. Scientists have demonstrated that the CRISPR/Cas9 system works in a wide range of organisms and cells, including human cells, plants, and model organisms such as flies, worms, and mice. Many Cornell scientists, in particular, are embracing the cutting-edge technology and testing its limits.

John C. Schimenti
Biomedical Sciences, College of Veterinary Medicine/Molecular Biology and Genetics, College of Agriculture and Life Sciences/College of Arts and Sciences.

Jennifer Doudna, Ph.D., of the University of California, Berkeley, and Emmanuelle Charpentier, Ph.D., of Hannover Medical School, Germany, and Umeå University, Sweden, discovered CRISPR when they were studying bacterial immunity.
Bacteria use special sequences in their genome, called clustered regularly interspaced short palindromic repeats (CRISPR), to guide a DNA-cutting enzyme called Cas9 to specific sequences of DNA. Bacteria use this system to recognize and destroy foreign DNA, such as attacking viruses. But the system, a DNA-cutting enzyme guided by an RNA molecule to a specific sequence, is exactly the tool needed to make sequence-specific edits in the DNA of a human cell.