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With transgenic technologies, he could insert foreign genes into a cell's genome, making the cell create whatever protein the gene called for. Tsien searched for a gene that encoded a fluorescent protein he could monitor—a daunting challenge. He remembered reading a review of a protein called aequorin, which is produced by the Aequorea victoria jellyfish in the Puget Sound. “[The paper] said if you're really careful, you can get rid of this awful contaminant, green fluorescent protein,” Tsien recalls. “In despair, I typed green fluorescent protein into Medline in early 1992.”
The rest, as they say, is history. He found that a scientist at the Woods Hole Oceanographic Institution, Douglas Prasher, had just cloned the gene for GFP. When Tsien contacted him, Prasher said his funding was ending and he was stopping work on it, but he agreed to send the DNA for GFP to Tsien. Another scientist, Martin Chalfie also contacted Prasher and received the DNA.
Would the gene only work in the jellyfish? If GFP needed to interact with other chemicals in jellyfish cells in order to glow, it wouldn't solve Tsien's problem; he needed a protein he could add to any cell. Chalfie quickly answered that question by creating transgenic bacteria and worms that glowed, showing GFP would glow in other organisms as well.
Tsien immediately recognized the potential of GFP, but he also saw its flaws—it gave a big peak in the UV spectrum where scientists didn't want to illuminate; the visible blue-green peak was much smaller. And in its native state, five-sixths of it was in a form useless to researchers. He modified the gene, creating a series of highly effective fluorescent proteins in colors from blue to red.
And that Midwestern questioner will be happy to know Tsien's lab has made progress toward producing an infrared fluorescent protein for viewing cells and organs inside living animals without having to open the animals. (The deep red color of blood obscures the current palette of fluorescent proteins.)
The Nobel Prize can only be split three ways, but Tsien has been adamant about recognizing the contribution of Prasher, who eventually left science and now lives in Huntsville, Alabama.
“If there's anyone who's underappreciated, it's Douglas Prasher,” Tsien says. “If he hadn't cloned the GFP gene, progress in the field would have been delayed indefinitely. I don't know anyone else who was working on the cloning.” Tsien and Chalfie flew Prasher and his wife Virginia Eckenrode to Sweden for the Nobel ceremony.
“Seeing things, that's sort of buried in my psychic makeup,” says Tsien, explaining why his work is so focused on visualization. Today, he's applying that inner aesthetic to new problems.
“How and where synapses adapt to create and preserve a memory is one of the most important problems in neurobiology right now,” says Michael Lin, a postdoctoral researcher in Tsien's lab. When new memories form, unique neural connections, or synapses, grow in size. This process involves new protein production, so Lin and Tsien are working on ways to watch the proteins that are created during synapse growth.