““The bacterial defense system was soon found to involve at least two critical components. The first piece was the "seeker"-an RNA encoded in the bacterial genome that matched and recognized the DNA of the viruses. The principle for the recognition, yet again, was binding: the RNA "seeker" was able to find and recognize the DNA of an invading virus because it was a mirror image of that DNA-the yin to its yang. It was like carrying a permanent image of your enemy in your pocket-or, in the bacteria's case, an inverted photograph, etched indelibly into its genome. The second element of the defense system was the "hitman." Once the viral DNA had been recognized and matched as foreign (by its reverse-image), a bacterial protein named Cas9 was deployed to deliver the lethal gash to the viral gene. The "seeker" and the "hitman" worked in concert: the Cas9 protein delivered its cuts to the genome only after the sequence had been matched by the recognition element. It was a classic combination of collaborators-spotter and executor, drone and rocket, Bonnie and Clyde.””
