STOCKHOLM, Sweden (AP) _ Americans Andrew Z. Fire and Craig C. Mello won the Nobel Prize in physiology or medicine Monday for discovering a powerful way to turn off the effect of specific genes, opening a new avenue for disease treatment.
``RNA interference'' is already being widely used in basic science as a method to study the function of genes and it is being studied as a treatment for infections such as the AIDS and hepatitis viruses and for other conditions, including heart disease and cancer.
Fire, 47, of Stanford University, and Mello, of the University of Massachusetts Medical School in Worcester, published their seminal work in 1998.
RNA interference occurs naturally in plants, animals, and humans. The Karolinska Institute in Stockholm, which awarded the prize, said it is important for regulating the activity of genes and helps defend against viral infection.
``This year's Nobel laureates have discovered a fundamental mechanism for controlling the flow of genetic information,'' the institute said.
Erna Moller, a member of the Nobel committee, said their research helped shed new light on a complicated process that had confused researchers for years.
``It was like opening the blinds in the morning,'' she said. ``Suddenly you can see everything clearly.''
Genes produce their effect by sending molecules called messenger RNA to the protein-making machinery of a cell. In RNA interference, certain molecules trigger the destruction of RNA from a particular gene, so that no protein is produced. Thus the gene is effectively silenced.
For instance, a gene causing high blood cholesterol levels was recently shown to be silenced in animals through RNA interference.
Mello, reached at his home in Shrewsbury, Mass., said the award came as a ``big surprise.''
``I knew it was a possibility, but I didn't really expect it for perhaps a few more years. Both Andrew and I are fairly young, 40 or so, and it's only been about eight years since the discovery.''
He said he would try to get into work Monday but expected to accomplish ``not a lot.''
Fire, who conducted the research while at the Carnegie Institution, said he was honored that the work ``has received such positive attention.''
``Science is a group effort. Please recognize that the recent progress in the field of RNA-based gene silencing has involved original scientific inquiry from research groups around the world,'' he said in a statement released by the Washington-based Carnegie Institution.
The announcement opened this year's series of prize announcements. It will be followed by Nobel prizes for physics, chemistry, literature, peace and economics.
Last year's medicine prize went to Australians Barry J. Marshall and Robin Warren for discovering that bacteria, not stress, causes ulcers.
The Nobel committees do not reveal who has been nominated for the awards, but that does not stop experts and Nobel-watchers from speculating on potential winners.
Alfred Nobel, the Swedish inventor of dynamite, established the prizes in his will in the categories of literature, peace, medicine, physics and chemistry. The economics prize is technically not a Nobel but a 1968 creation of Sweden's central bank.
Winners receive a check of $1.4 million, handshakes with Scandinavian royalty, and a banquet on Dec. 10 _ the anniversary of Nobel's death in 1896. All prizes are handed out in Stockholm except for the peace prize, which is presented in Oslo.