In her 2011 paper Charpentier showed that tracrRNA was required for producing the crRNA guide. She later said that she suspected it played an even larger, ongoing role, though that possibility had not been part of their initial round of experiments. When those experiments failed, Chylinski decided to throw tracrRNA into his test-tube mix. It worked: the three-component complex reliably chomped up the target DNA. Jinek immediately told Doudna the news: “Without the tracrRNA, the crRNA guide does not bind to the Cas9 enzyme.”
