(1947–    ), Israeli biochemist and Nobel laureate. Born on Oct. 1, 1947, in Haifa, Israel, he received a master of science degree in 1971 and an M.D. in 1974 from the Hadassah Medical School of the Hebrew University of Jerusalem and a doctor of science degree in medicine in 1982 from the Technion–Israel Institute of Technology in Haifa. He subsequently became a professor at the biochemistry unit and director of the Rappaport Family Institute for Research in Medical Sciences at the Technion.

In the late 1970s and early 1980s Ciechanover, in collaboration with his mentor Avram Hershko and U.S. scientist Irwin Rose, made fundamental discoveries concerning a process that previously had been relatively little studied but was crucial to the normal functioning of biological cells: the “degradation,” or destruction, of proteins that are faulty or that have outlived their usefulness and are no longer needed. The three researchers discovered that a polypeptide molecule called ubiquitin plays a key role in protein degradation. (Polypeptides are the chains of amino acids that make up protein; the molecule's name ubiquitin reflects the fact that it was identified in numerous organisms and seemed to be rather ubiquitous.) It was found that ubiquitin molecules bind, with the help of special enzymes, to unwanted proteins, thereby marking the proteins for destruction. Proteins labeled with ubiquitin are accepted into a structure called the proteasome, where they are chopped up into pieces. In addition to quality control of newly synthesized proteins, ubiquitin-mediated protein degradation is important in such activities as cell division, DNA repair and transcription, and the body's immune defenses against disease (see also Immune System). A breakdown in the protein degradation process can cause such serious disorders as cervical cancer and cystic fibrosis. The discoveries made by Ciechanover and his colleagues paved the way for researchers to begin developing therapeutic drugs targeting aspects of the ubiquitin system.

Ciechanover, Hershko, and Rose each were awarded a one-third share of the 2004 Nobel Prize in chemistry for “the discovery of ubiquitin-mediated protein degradation.”

Ciechanover and Hershko, in recognition of their work on the ubiquitin-mediated protein degradation system, received the Albert Lasker Basic Medical Research Award in 2000.