STOCKHOLM, Sweden - Israelis Aaron Ciechanover and Avram Hershko and American Irwin Rose won the 2004 Nobel Prize in chemistry today for discovering a process that lets cells destroy unwanted proteins.

When the process goes wrong, several hundred diseases can result, including cervical cancer and cystic fibrosis. So the work provides the basis for developing new therapies.

The Royal Swedish Academy of Sciences honored Ciechanover, 57, Hershko, 67, and Rose, 78, for their work in the 1980s that discovered that cells give a chemical "kiss of death" to proteins that must be destroyed.

The marked proteins are then chopped to pieces. The protein-destroying process, called "ubiquitin-mediated protein degradation," governs such key processes as cell division, DNA repair, quality control of newly-produced proteins, and important parts of the immune defense, the academy said in its citation.

Ciechanover is director of the Rappaport Family Institute for Research in Medical Sciences at the Technion, in Haifa, Israel, while Hershko, originally from Hungary, is a professor there.

Rose is a specialist at the department of physiology and biophysics at the college of medicine at the University of California-Irvine.