<figcaption> Credit: COURTESY OF LEEMOR JOSHUA-TOR</figcaption>

Greg Hannon's group at Cold Spring Harbor Laboratory was one of many labs scrambling to identify Slicer, the enzyme doing the cutting in RNA-mediated interference. Using biochemical mutagenesis, in vivo knockouts, and enzymatic assays, they had all but pegged Argonaute2. But, says Hannon, "We were stuck ? We could go right up to the edge of saying it was Argonaute without actually saying it."

Just before he accepted defeat, however, a CSHL colleague, Leemor Joshua-Tor, invited him into a darkened room and gave him a pair of 3D glasses. She'd solved the crystal structure of Argonaute, and it revealed a structural homology to RNAse H providing guidance for targeted mutagenesis. "There's just no substitute for when you see it sitting there in 3D," Hannon says. The labs published their milestone findings together in 2004.1,2 "Crystal structures are often important for establishing biological...


1. J. Song et al., "Crystal structure of Argonaute and its implications for RISC Slicer activity," Science, 305:1434-7, 2004. (Cited in 140 papers) 2. J. Liu et al., "Argonaute2 is the catalytic engine of mammalian RNAi," Science, 305:1437-41, 2004. (Cited in 180 papers)

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