Aziz Sancar: How a Cell Repairs Itself
In 1977 a Turkish physician with a fresh American doctorate took a job at Yale as a laboratory technician. He had already tried the United States once, four years earlier, and gone home defeated. From that technician's bench he spent five years working out the molecular machinery by which a living cell finds damage in its own DNA and cuts it out. In 2015 that work took him to Stockholm.
Savur
Aziz Sancar was born on 8 September 1946 in Savur, in Mardin Province in Turkey's far southeast, the seventh of eight children. His parents were uneducated and insisted their children would not be. He spoke Arabic with them and Turkish with his brothers and sisters. The family produced more than one public figure: his eldest brother Kenan became a brigadier general in the Turkish Armed Forces, and the politician Mithat Sancar is his second cousin.
He went to Istanbul University's Faculty of Medicine and graduated at the top of his class in 1969 with an MD. Medicine, though, was not where he stopped. He wanted the chemistry underneath it.
A False Start and a Second Try
In 1973 Sancar came to the United States for postdoctoral work at Johns Hopkins. He lasted about eighteen months before difficulties adapting sent him back to Turkey. It is the sort of retreat that ends most scientific careers. It did not end his.
He returned and enrolled at the University of Texas at Dallas under Claud Stan Rupert, taking his PhD in 1977 with a dissertation on the photoreactivating enzyme — DNA photolyase — of *Escherichia coli*. In 1976, during that doctoral work, he cloned the photolyase gene. The enzyme it encodes uses visible light to undo one of the commonest forms of genetic damage: the thymine dimers that ultraviolet radiation welds into DNA. Sancar would chase photolyase for the next twenty years, until he had directly observed the radicals of its photocycle — the reaction caught in the act.
Twenty questions, eight minutes on the clock, and a percentile measured against everyone who has taken it. No sign-up.
Take the IQ test →That same year, 1978, he married Gwen Boles, whom he had met during his doctoral studies; she became a professor of biochemistry and biophysics in her own right.
The Technician at Yale
No one offered the newly minted PhD a faculty position. From 1977 to 1982 he worked at Yale, initially as a laboratory technician, and did the science that would define the field.
He identified the UvrABC endonuclease and showed exactly what it does. Confronted with a damaged stretch of DNA, the enzyme complex cuts the damaged strand twice — on both sides of the lesion — excising a segment of twelve to thirteen nucleotides containing the damage. The gap is then filled from the intact complementary strand. This is nucleotide excision repair, and Sancar had reduced it from a phenomenon to a mechanism: a specific set of proteins, a specific pair of incisions, a countable number of bases removed.
The implications reach directly into human disease. Cells that cannot perform this excision cannot survive sunlight without accumulating mutations; the same logic governs how tumours resist chemotherapy drugs that work by damaging DNA. Understanding repair is understanding both why cancer starts and why it sometimes cannot be killed.
Chapel Hill
In 1982 the University of North Carolina at Chapel Hill hired him. He never left. He became the Sarah Graham Kenan Professor of Biochemistry and Biophysics and a member of the UNC Lineberger Comprehensive Cancer Center. In 2005 he was elected to the US National Academy of Sciences — its first Turkish member.
His later work returned to light from a different angle. With colleagues he established that the Period and Cryptochrome genes govern the human circadian clock, publishing the findings in *Genes and Development* in September 2014. Cryptochromes are photolyase relatives: the same protein family that repairs sunlight damage also tells the body what time of day it is.
Recognition
The National Science Foundation gave him a Presidential Young Investigator Award in molecular biophysics in 1984. TÜBİTAK's Science Award followed in 1995 and the Vehbi Koç Award in 2007. In 2015 he shared the Nobel Prize in Chemistry with Tomas Lindahl and Paul L. Modrich for mechanistic studies of DNA repair. He is an honorary member of the Turkish Academy of Sciences and the American Academy of Arts and Sciences, and in January 2025 received the Order of Cultural Ambassador of the Turkic World.
On 19 May 2016 he did something no other laureate has done: he donated his original Nobel medal and certificate to Anıtkabir, Atatürk's mausoleum in Ankara, delivering a replica to Istanbul University. With his wife he founded the Aziz and Gwen Sancar Foundation and the Carolina Türk Evi near the UNC campus, providing housing and scholarly exchange for Turkish students in America.
Identity
The prize brought scrutiny of his ethnic origins, and it plainly irritated him. Asked by the BBC whether he was a Turk or half-Arab, he recalled: "I told them that I neither speak Arabic nor Kurdish and that I was a Turk. I'm a Turk, that's it." On religion he has been equally direct and more melancholy: "I am proud to be Muslim, but I can not state this fact in many regions of the United States due to ongoing issues." He holds Turkish, American and Turkish Republic of Northern Cyprus citizenship, the last granted in July 2025.
Why Sancar Matters
Every cell in every organism sustains thousands of DNA lesions a day and survives because it repairs them. Before Sancar, that was a description. After him, it was a set of named enzymes performing measurable cuts at defined positions. He built the picture from a technician's bench, having already been sent home from America once, and he built it so thoroughly that the chemistry of cancer, ageing and sunlight all now start from his diagrams.
