Eventually, Krzysztof and Martin performed experiments in which they included not only the CRISPR RNA but also the second type of RNA, called tracrRNA, that Emmanuelle’s lab had found to be required for production of CRISPR RNAs in S. pyogenes. The result was simple but, to us, electrifying: DNA bearing a perfect match to twenty letters in the CRISPR RNA molecule was cleanly cut apart.
