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What are the key components of the CRISPR-Cas9 system that are activated (set into motion) when a virus invades a bacterium?

CRISPR-Cas9 was adapted from a naturally occurring genome editing system in bacteria. ... As in bacteria, the modified RNA is used to recognize the DNA sequence, and the Cas9 enzyme cuts the DNA at the targeted location. Although Cas9 is the enzyme that is used most often, other enzymes (for example Cpf1) can also be used.

Some bacteria? have a similar, built-in, gene editing system to the CRISPR-Cas9 system that they use to respond to invading pathogens like viruses, much like an immune system.