" It turns out that tracrRNA performs two important tasks. First, it facilitates the making of the crRNA, the sequence that carries the memory of a virus that previously attacked the bacteria. Then it serves as a handle to latch on to the invading virus so that the crRNA can target the right spot for the Cas9 enzyme to chop. "

― Walter Isaacson , The Code Breaker: Jennifer Doudna, Gene Editing, and the Future of the Human Race