CRISPR Turns a Bacterial Defense into a Gene-Editing Tool

In 2012, researchers led by Jennifer Doudna at the University of California, Berkeley, and Emmanuelle Charpentier at Umeå University published a method that repurposed a natural bacterial immune system into a programmable gene-editing technology. Earlier investigations into microbial defenses had traced how clustered regularly interspaced short palindromic repeats worked alongside Cas enzymes. Alexander Bolotin's team described the protein now known as Cas9 in 2005, and in 2007 Rodolphe Barrangou and Philippe Horvath demonstrated experimentally that bacteria capture fragments of bacteriophage DNA to fend off future viral attacks. The 2012 advance showed that pairing the Cas9 nuclease from Streptococcus pyogenes with customizable synthetic guide RNA enabled researchers to direct molecular cuts to specific sequences of DNA.

Earlier genetic engineering methods in eukaryotic cells had existed since the 1980s, but they remained difficult to implement on a routine basis. Technologies developed in the 2000s, such as zinc finger nucleases and transcription activator-like effector nucleases, required researchers to design and manufacture entirely new proteins for each target sequence. CRISPR-Cas9 fundamentally changed laboratory workflows because targeting required only the synthesis of a short RNA guide that bonded with complementary DNA base pairs adjacent to a protospacer motif. This simplified mechanism offered a comparatively inexpensive way to target multiple genetic sites at once and achieve irreversible gene knockouts.