Osamu Shimomura, a Japanese citizen who works in the United States, and Americans Martin Chalfie and Roger Tsien shared the chemistry prize for discovering and developing green fluorescent protein, or GFP.
When exposed to ultraviolet light, the protein glows green. It can act as a marker on otherwise invisible proteins within cells to trace them as they go about their business. It can tag individual cells in tissue. And it can show when and where particular genes turn on and off.
Researchers worldwide now use GFP to track development of brain cells, the growth of tumors and the spread of cancer cells. It has let them study nerve cell damage from Alzheimer's disease and see how insulin-producing beta cells arise in the pancreas of a growing embryo, for example.
In awarding the prize, the Royal Swedish Academy compared the impact of GFP on science to the invention of the microscope. For the past decade, the academy said, the protein has been "a guiding star " for scientists.
GFP's chemical cousins produce other colors, which let scientists follow multiple cells or proteins simultaneously.
"This is a technology that has literally transformed medical research," said Dr. John Frangioni, an associate professor of medicine and radiology at Harvard Medical School. "For the first time, scientists could study both genes and proteins in living cells and in living animals."
Last year, in what the Nobel citation called a "spectacular experiment," Harvard researchers announced that they had tagged brain cells in mice with some 90 colors. The technique is called "Brainbow."
GFP was first discovered by Shimomura at Princeton University. He'd been seeking the protein that lets a certain kind of jellyfish glow green around its edge. In the summer of 1961, he and a colleague processed tissue from about 10,000 jellyfish they'd collected near the island town of Friday Harbor, Wash. The next year, they reported the finding of GFP.
Some 30 years later, Chalfie showed that the GFP gene could make individual nerve cells in a tiny worm glow bright green.
Tsien's work provided GFP-like proteins that extended the scientific palette to a variety of colors. Tsien "really made it a tool that was extremely useful to lots of people," Chalfie told reporters.
Shimomura, 80, now works at the Marine Biological Laboratory in Woods Hole, Mass., and the Boston University Medical School. Chalfie, 61, is a professor at Columbia University in New York, while Tsien, 56, is a professor at the University of California, San Diego, and an investigator with the Howard Hughes Medical Institute.
The trio will split the $1.4 million award.
Chalfie said he slept through the Nobel committee's phone calls early Wednesday because he'd accidentally adjusted his telephone to ring very softly. He found out about the prize only when he checked the Nobel Web site to see who had won.
"It's not something out of the blue, but you never know when it's going to come or if it's going to come, so it's always a big surprise when it actually happens," Chalfie said.
Shimomura told reporters that he, too, was surprised.
"My accomplishment was just the discovery of a protein. ... But I am happy," he said.
Speaking to reporters by telephone, Tsien thanked scientists worldwide. When they do "good things with GFP and its progeny," Tsien said he can "bask in the warmth of that glow a little bit too."
Gunnar von Heijne, the chairman of the chemistry prize committee, demonstrated the award-winning research to reporters by shining ultraviolet light on a tube with E. coli bacteria containing GFP. The tube glowed green.
Von Heijne said that kind of result "gets scientists' hearts beating three times faster than normal."
The winners of the Nobel Prizes in medicine and physics were presented earlier this week. The prizes for literature, peace and economics are due to be announced Thursday, Friday and Monday.
Three Americans, three Japanese, two French and one German researcher have won Nobel Prizes so far this year.
The awards include the money, a diploma and an invitation to the prize ceremonies in Stockholm and Oslo on Dec. 10, the anniversary of prize founder Alfred Nobel's death in 1896.