To do the targeting, he harnessed a family of ubiquitous, naturally occurring proteins called zinc finger proteins, so named because they recognized DNA using fingerlike extensions held together by zinc ions and arranged side by side, just like the fingers of a hand. Because these zinc finger proteins were built of multiple repeated segments arranged in tandem, with each segment recognizing a specific three-letter DNA sequence, it seemed likely that scientists could redesign the proteins to recognize various DNA sequences by combining segments in different ways.
