technology—at least, the first version of it—was discovered in 2009 and came from studies of novel types of proteins found in Xanthomonas, a pathogenic plant-infecting bacterium. Called transcription activator–like effectors, or TALEs, these proteins are remarkably similar to zinc finger proteins in their construction: they’re built out of multiple repeating segments in which each segment recognizes a given area of DNA. But there is a difference: whereas each finger of the zinc finger proteins recognizes a three-letter sequence of DNA, each segment in TALEs recognizes just a single letter of
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