Hungarian-born Israeli biochemist who shared the 2004 Nobel Prize for Chemistry with Aaron J. Ciechanover (Ciechanover, Aaron J.) and Irwin Rose (Rose, Irwin) for their joint discovery of the mechanism by which the cells of most living organisms remove unwanted proteins.

Hershko's family emigrated from Hungary to Israel. He studied at the Hebrew University–Hadassah Medical School in Jerusalem, receiving an M.D. (1965) and a Ph.D. (1969). In 1972 he joined the faculty of the Technion–Israel Institute of Technology in Haifa, where Ciechanover was one of his students. Hershko became a distinguished professor at the Technion in 1998.

In the late 1970s and early '80s, Hershko and Ciechanover worked with Rose at the Fox Chase Cancer Center in Philadelphia. There the three scientists did much of their prizewinnning research on how cells degrade, or destoy, the proteins that are no longer useful. The process begins when a molecule called ubiquitin (from the Latin ubique, meaning “everywhere,” because it occurs in so many different cells and organisms) attaches itself to the protein targeted for destruction. It then accompanies the protein to a proteasome, which is essentially a structure of powerful enzymes that break the protein into its component amino acids. The outer membrane of the proteasome admits only proteins carrying a ubiquitin molecule, which detaches before entering the proteasome and is reused.

Hershko, Ciechanover, and Rose also demonstrated that ubiquitin-mediated protein degradation helps control a number of other critical biochemical processes, including cell division, the repair of defects in DNA, and gene transcription, the process in which genes use their coded instructions to manufacture a protein. Diseases such as cystic fibrosis result when the protein-degradation system does not work normally, and researchers hoped to use the findings to develop drugs for the treatment of such illnesses.