Americans Andrew Fire and Craig Mello won the Nobel Prize in physiology and medicine yesterday for discovering a method of controlling the flow of genetic information.

Their method is an important research tool scientists hope will lead to new treatments for a range of illnesses, from viruses to cancer.

The Karolinska Institute in Stockholm honoured the pair for their discovery of "RNA interference - gene silencing by double-stranded RNA," a process that has the potential to help researchers eliminate genes that can trigger high blood cholesterol levels and fight other diseases.

RNA interference occurs in plants, animals, and humans. The institute said it was of great importance for the regulation of gene expression, participates in defence against viral infections, and keeps jumping genes under control.

RNA interference is already being widely used in basic science as a method to study the function of genes and it may lead to novel therapies in the future.

Fire, of the Massachusetts Institute of Technology, and Mello, of Harvard University, were born in 1959 and 1960, respectively.

"This year's Nobel Laureates have discovered a fundamental mechanism for controlling the flow of genetic information. Our genome operates by sending instructions for the manufacture of proteins from DNA in the nucleus of the cell to the protein synthesising machinery in the cytoplasm. These instructions are conveyed by messenger RNA," the institute said. Fire and Mello published their discovery of a mechanism that can degrade mRNA from a specific gene in 1998.