Two more US scientists, Craig Mello and Andrew Fire were awarded the Nobel prize in Medicine for their work on RNA interference that can silence genes and alter a cell's function.
The Royal Swedish Academy of Sciences in Stockholm said on Tuesday that Smoot and Mather had been rewarded "for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation (CMB)."
Scientists say CMB is the "oldest light" in the universe and tells us about the evolution of the cosmos.
The two men's work was based on measurements that were made with the help of the COBE satellite launched by Nasa in 1989.
The information received from the satellite was crucial in gathering increased support for the Big Bang theory of the beginning of the universe.
Mather, 60, works at the Nasa Goddard Space Flight Center in Greenbelt, Maryland, and Smoot, 61, works at the Lawrence Berkeley National Laboratory in Berkeley, California.
"The very detailed observations that the laureates have carried out from the COBE satellite have played a major role in the development of modern cosmology into a precise science," the academy said in its citation.
Mello's discovery enables genes
to be switched off
Fire and Mello were rewarded for the discovery that little pieces of genetic material, called RNA, could silence genes - turning them off and altering a cell's functions.
Plants use the mechanism to fight off viruses and the discovery is being exploited by laboratories and companies around the world to try to find cures for everything from cancer, to certain types of blindness, and even bird flu.
"It's a classic example of basic research which has turned out to uncover a biological mechanism which now has tremendous potential for ... really impacting human health," said Dr Jeremy Berg, head of the US National Institute of General Medical Sciences, which funded Fire and Mello's work.
Less than a decade after Mello and Fire made their discovery in 1997, trials using RNA interference, or RNAi, to treat people are already under way.
RNA interference appears to help regulate which genes turn on and off as an embryo develops, and may play a role in cancer and other diseases, according to the Howard Hughes Medical Institute, which supports Mello in his lab at the University of Massachusetts Medical School.
Phillip Sharp of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, himself a 1993 Nobel Prize winner, has used RNAi to kill HIV, the virus that causes AIDS.
Many companies are using RNA interference to try to treat disease, and a little industry has also sprung up to provide researchers with products using pre-packaged RNAi-silenced genes for their research.