Researchers had shown that if you deactivated Cas9 in bacteria, the CRISPR system no longer cut up the invading viruses. They had also established the essential role of another part of the complex: CRISPR RNAs, known as crRNAs. These are the small snippets of RNA that contain some genetic coding from a virus that had attacked the bacteria in the past. This crRNA guides the Cas enzymes to attack that virus when it tries to invade again. These two elements are the core of the CRISPR system: a small snippet of RNA that acts as a guide and an enzyme that acts as scissors.
