Test tubes containing various fluorescent proteins developed by scientist Roger Tsien are shown Wednesday in this photo released by the University of California-San Diego. Tsien and scientists Osamu Shimomura and Martin Chalfie won the Nobel Prize in chemistry Wednesday for their research on proteins.

Three U.S.-based scientists won a Nobel Prize on Wednesday for turning a glowing green protein from jellyfish into a revolutionary way to watch the tiniest details of life within cells and living creatures.

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 with 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.

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.

The trio will split the

$1.4 million award.