Nobel Prize in Medicine shared by Harvard Medical School professor

Nearly three decades ago, Szostak began to collaborate with Blackburn, looking at the tips of the chromosome of a single-celled, pond-dwelling organism called Tetrahymena. They spliced the sequence of nucleotides they saw in the Tetrahymena into yeast and found that it played a protective function in a completely different organism.

What they discovered would turn out to be fundamental to biology. The telomeres, the tips of chromosomes, have been compared to the plastic tips on the ends of shoelaces, which prevent the lace from unraveling. They are now known to play a role in protecting DNA against degradation in most plants and animals.

Blackburn and Greider isolated telomerase, the enzyme that builds the protective caps on the tips of chromosomes. Szostak found a protein that was a key component of the enzyme.

For years, science has built on this work. Normally, in adult cells the activity of the enzyme is shut off, and telomeres shorten as aging occurs. In cancer, the activity of the enzyme is overactive, giving cells immortality. That meant the enzyme was a potential drug target, since it has been found to be overactive in the vast majority of human tumors.

In a 2006 profile in the Globe, Szostak spoke about the work he did on telomeres and the enzyme that builds them. "If you don't have that enzyme, your DNA gets shorter and shorter," Szostak said. "This can cause chromosome rearrangements and breakage and all kinds of problems, including cancer. ... You can never tell at the time that your work is going to affect so many things."

It was the first time that two women have been among the winners of the medicine prize, Nobel committee members said.

Blackburn, who holds U.S. and Australian citizenship, is a professor of biology and physiology at the University of California, San Francisco. Greider is a professor in the department of molecular biology and genetics at Johns Hopkins University School of Medicine in Baltimore.

Greider, 48, said she was telephoned just before 5 a.m. her time with the news that she had won.

"It's really very thrilling, it's something you can't expect," she told The Associated Press by telephone.

People might make predictions of who might win, but one never expects it, she said, adding that "It's like the Monty Python sketch, 'Nobody expects the Spanish Inquisition!' "

Greider described the research as beginning with experiments aimed at understanding how cells work, not with the idea for certain implications for medicine.

"Funding for that kind of curiosity-driven science is really important," she said, adding that disease-oriented research isn't the only way to reach the answer, but "both together are synergistic."

Blackburn, 60, said she was awakened at 2 a.m.

"Prizes are always a nice thing," she told the AP. "It doesn't change the research per se, of course, but it's lovely to have the recognition and share it with Carol Greider and Jack Szostak."

In addition to his work on telomeres, Szostak has been investigating the origins of life, in the emerging field of astrobiology.

Material from the Associated Press was used in this report.