What is the role of Cas9 in the CRISPR system?

Cas9 plays a crucial role in the CRISPR system by acting as a cutting enzyme, or endonuclease, that can locate and cleave specific sequences of DNA, typically within the context of defending against viral infections in bacteria. When the CRISPR system recognizes viral genetic material, Cas9 is guided by a specific RNA molecule (derived from the CRISPR array) that matches the viral DNA sequence. Upon binding to this target, Cas9 introduces double-strand breaks in the DNA, effectively inactivating the viral DNA and preventing it from replicating and causing infection. This ability to cut DNA has been harnessed in gene editing technologies, making Cas9 a powerful tool for altering genetic material in various organisms.