Washington - Martin Chalfie, a professor of biological sciences at Columbia University in New York, and Roger Y Tsien, a professor of pharmacology at the University of California in San Diego, were among three scientists awarded the Nobel prize for chemistry on Wednesday.

Chalfie, Tsien and Osamu Shimomura shared the prize for discovering and developing green fluorescent protein (GFP) a key tool used for tagging bioscience processes. It can illuminate growing cancer tumours, show the development of Alzheimer's in the brain or the growth of pathogenic bacteria.

With GFP, scientists can follow the machinery inside individual cells - a complicated mix of proteins, fatty acids, carbohydrates and other molecules that cannot be viewed through an ordinary microscope.

In the 1960s, when Shimomura began studying the bioluminescent jellyfish Aequorea victoria - whose outer edge glows green when the creature is agitated - he had no idea it would lead to a scientific revolution.

In 1988, Chalfie heard about GFP for the first time at a seminar at Columbia. He had so far been dealing with the millimetre-long roundworm Caenorhabditis elegans, which despite having only 959 cells, has a brain, mates and grows old.

It is one of the most frequently studied organisms in the world also because it is transparent and easy to observe under a microscope, and a third of its genes are related to human genes.

Chalfie realised that GFP would be a fantastic tool for mapping the roundworm and "demonstrated the value of GFP as a luminous genetic tag for various biological phenomena," the Royal Swedish Academy of Sciences said.

Chalfie was born in 1947 and grew up in Chicago. He earned his PhD in neurobiology from Harvard University in 1977. He has been a William R Kenan Jr Professor of Biological Sciences at Columbia University since 1982.

In his 25th anniversary report on graduating from Harvard, Chalfie said he endured three years of odd jobs and finally "started what has turned into a real job: Biological research."

He lauded his doctoral adviser Bob Perlman and post-doctoral colleagues "who by their example and enthusiasm made me strive to do significant research and to try to avoid any self-imposed barriers," according to Harvard magazine.

"They also taught me that sharing, not hoarding, information was the most satisfying way of operating in this business," Chalfie wrote.

Ten years later he commented that "Life and lab continue to be pretty enjoyable."

Taking Chalfie's work further, Tsien stepped in and extended the palette with many new colours that glowed longer and with higher intensity.

He was able to develop new variants of GFP that shone more powerfully and in different colours such as cyan, blue and yellow. It's because of this that researchers today can mark different proteins in different colours and watch how they interact.

Tsien was born in 1952 in New York. He earned a PhD in physiology from Britain's Cambridge University in 1977. He has been in San Diego since 1989.