Aziz Sancar: DNA Repair, the Body Clock and the Nobel
Aziz Sancar, born in Savur in 1946, shared the 2015 Nobel Prize in Chemistry for DNA repair. His life and his science in plain words, with photos.
Table of Contents
Aziz Sancar is a biochemist and doctor from Savur, a town in Mardin province in south-eastern Türkiye, born on 8 September 1946. In 2015 he shared the Nobel Prize in Chemistry with Tomas Lindahl and Paul Modrich for mapping how cells repair damaged DNA. He worked out how cells fix the damage that ultraviolet (UV) light does to DNA, and he found two proteins that help run the body clock.
The short version
A doctor from Savur who mapped how cells repair DNA and won the 2015 Nobel Prize in Chemistry.
- Born: 8 September 1946 in Savur, Mardin province. He was the seventh of eight children.
- The prize: the 2015 Nobel Prize in Chemistry, shared with Tomas Lindahl and Paul Modrich, one third each, “for mechanistic studies of DNA repair”. It was announced on 7 October 2015.
- His part: nucleotide excision repair, the way a cell cuts a short stretch of damaged DNA out and patches the gap. His lab found the two cuts in 1982.
- The clock: his lab named and studied the cryptochromes, light-sensing proteins that help run the 24-hour body clock.
- Today: professor at the University of North Carolina at Chapel Hill since 1982. His wife, Gwen Sancar, is also a professor of biochemistry and biophysics.
DNA is a long ladder whose steps are made of four chemical letters, A, T, G and C. Sunlight can damage it: UV light can weld two T letters side by side into a lump. Sancar spent his career on how cells mend damage like this. The bench below damages a strand and mends it by the two routes his work covers.
Try it: the repair bench
Damage a strand with UV, then mend it
Two T letters of the top strand are stuck together by UV light. Pick the spot, the cell and the way it is mended, then step through the repair. The log card can be copied as notes.
Damage
UV light has welded two neighbouring T letters on the top strand into a lump, a thymine dimer. The strand is bent at letters 28 and 29. The bottom strand is intact.
Repair log
- Cell
- Bacterium
- Damage
- Two T letters welded by UV (a thymine dimer), spot 2 of 3, letters 28 and 29
- Route
- Cut and patch (excision repair)
- Letters taken out
- None yet
- Step
- 0 of 5: Damage
- Found by
- Sancar’s lab, spring 1982 (paper 1983)
The five steps of cut and patch
- Spot. Three proteins run along the DNA and stop at the bent spot.
- Two cuts. They cut the damaged strand 7 letters to the left of the lump and 3 or 4 to the right.
- Piece out. The piece of 12 or 13 letters, with the lump in it, leaves.
- Patch. The gap is filled with new letters that match the bottom strand.
- Sealed. The last link is closed and the strand is whole again.
The Nobel Prize, in plain words
Every cell of the body holds a copy of the same DNA, and the order of its letters is the instruction book of the cell. That book is damaged all the time. UV light, cigarette smoke and plain chemistry change letters or break them, thousands of times a day, and the body copies the whole book several million times a day when cells divide.
The 2015 prize went to three scientists who each found a different part of the repair work. The Royal Swedish Academy of Sciences announced it on 7 October 2015, “for mechanistic studies of DNA repair”. The prize money, 8 million Swedish kronor, was shared equally.
Who fixes single letters that wear away?
In the early 1970s scientists thought DNA was very stable. Lindahl showed that it decays at a rate that ought to have made life on Earth impossible, and found how cells swap out a damaged letter.
Who cuts out damage that UV light has done?
Sancar mapped how cells cut a short stretch with UV damage out of one strand and patch the gap. The same route also mends damage from substances such as those in cigarette smoke.
Who checks the copy for mistakes?
Modrich showed how a cell corrects the errors made while DNA is copied. This check cuts the error rate by about a thousandfold.
- Tomas Lindahl
- Found the first of these repair enzymes, one that removes a damaged letter, in 1974. He pieced the process together over 35 years, and in 1996 he rebuilt the human version in a test tube.
- Paul Modrich
- Worked with the molecular biologist Matthew Meselson on the check that follows copying. In bacteria the old strand carries small chemical marks, so the cell can tell it from the new copy and corrects the copy; in people the check fixes all but one error in a thousand.
At the award ceremony
The presentation speech described the repair system as “a host of molecular repair mechanisms”, with “a swarm of proteins” watching over the genes. Sancar, it said, “has identified the components that build up this system and has explained in molecular detail how they work”. The cut-and-patch route works in a similar way in all living things, although the human version is more complex than the bacterial one.
The work matters beyond the laboratory. If one repair part fails, the genetic information changes quickly and the risk of cancer rises, and many cancers have switched one repair system off. Researchers try to use that weakness: blocking a repair system that is still working can slow the growth of such a cancer. People born with a fault in nucleotide excision repair are extremely sensitive to UV light.
Savur, Mardin and Istanbul, 1946 to 1969
Sancar was born on 8 September 1946 in Savur, the seventh of eight children. His father was a farmer, and the family had enough to eat but little else: the children had shoes only for school until the seventh grade. His mother could not read or write, but she insisted that every child went to school. His oldest brother, Kenan, taught him to read and write when he was five.
Trees and vegetables
Much of his childhood went into the family’s fruit and nut trees and vegetable garden in the valley below the house. He did not like the work.
Walls and walnuts
The garden terraces were held up by dry stone walls that needed constant mending, and the walnuts had to be shaken from the top of high trees.
Baby goats
Herding baby goats, which ran faster than a boy of five to seven.
Spring
The almond and plum trees flowering in the orchard.
Nights on the roof
On visits to an uncle in Mardin city he slept on the roof and watched the lights of two Syrian towns on the horizon.
School, then medicine
- Top of the class
- He was the top student in primary school in Savur and in secondary school in Mardin. His favourite classes were mathematics, Turkish, French and chemistry, and a chemistry teacher in the tenth grade made him want to become a chemist.
- Goalkeeper
- He played football as a goalkeeper, for Mardin Lisesi, Savur Spor and Mezopotamya Spor, and he was asked to take part in trials for the Turkish under-18 team. He stayed away, because he did not think his height and weight were enough for a national-level player, and he stopped playing after the tenth grade.
- November 1963
- He starts at the medical school in Istanbul. He had passed the entrance exams for both chemistry and medicine, and five friends from Mardin talked him into medicine.
- Second year
- A lecture on the double helix, the shape of DNA, makes up his mind: he will become a biochemist. He had come from the southeast determined to show that a student from there could finish at the top, so he gave almost all his time to study.
- June 1969
- He graduates at the top of his class. The head of the biochemistry department advises him to practise medicine for at least two years first, so he goes back to Savur.
- 1969 to 1971
- For six months he runs a free clinic in a room of the family house. When the Minister of Health passes through Savur and hears of it, he is offered a post with the ministry as chief medical officer of the village of Surgucu, with a Jeep and a driver.
From Surgucu he served nearby villages and some very remote ones. He was the first doctor many of his patients had ever seen, and he spent much of his salary on medicine for them and on toys for small children. He remembers those 18 months as the happiest time of his life.
Medicine still left him unsatisfied in one way. He wanted to know why streptomycin kills the tuberculosis bacterium and penicillin does not, and nobody he asked could tell him, so he kept applying for fellowships to study biochemistry abroad.
Abroad, 1971 to 1982
Baltimore
A NATO fellowship takes him to the United States, “because it was the leader in scientific research in the world”. He enters the biochemistry programme at Johns Hopkins University.
Baltimore
He leaves Johns Hopkins. He could not talk to professors or fellow students in English; he later wrote that it was like solitary confinement.
Savur, England
After about six months of medicine in Savur and a short time in England, he returns to the United States, now able to speak English well enough.
Dallas
He joins Claud Rupert’s laboratory at the University of Texas at Dallas, which had accepted him in 1973. Rupert found photolyase in 1958, the discovery that started the field.
Dallas
He wants to know how blue light revives bacteria given a deadly dose of UV. Nobody can make enough of the enzyme, so he plans to clone its gene.
Dallas
Six months of screening give him a bacterium with a broken copy of the gene. He clones it, phr, the first gene cloned east of the Rocky Mountains, he believes.
Türkiye
Four months of military service in Türkiye, as a Second Lieutenant.
Dallas
He defends his PhD in Dallas. Three leading DNA repair laboratories he applied to turn him down, he writes, probably because he had not yet published.
Yale
On Rupert’s recommendation Dean Rupp offers him a place at Yale, then one of the world’s three top DNA research centres. There he clones uvrA, uvrB and uvrC.
Yale
He publishes the maxicell method, a way to identify the proteins made by cloned genes. It is still his most cited paper.
Job search
About 50 universities turn him down. Then Mary Ellen Jones, chair of biochemistry at the University of North Carolina at Chapel Hill, calls with offers for him and his wife.
Yale
In a test tube with purified proteins he finds that the damaged strand is cut twice.
Chapel Hill
They move to Chapel Hill, and he starts experiments three days after arriving.
Gwen Sancar, the other scientist in the family
Gwen Boles was a graduate student in the same department in Dallas, and the two became close friends. She finished three months before he did and took a research post in New York, on the molecular basis of thalassemia, a blood disease. They married in 1978. Two years later she joined Dean Rupp’s laboratory at Yale to work on how the cell controls the genes that repair DNA.
“Aziz, I don’t think you would have survived without Gwen.”
One of his mentors, quoted in his Nobel biography, where he also thanks her “for her love and support”.
Today she is a professor of biochemistry and biophysics and, with him, a co-founder of the Aziz and Gwen Sancar Foundation.
DNA repair, in plain words
When two T letters sit side by side on one strand, UV light can weld them into a lump, called a thymine dimer. The strand bends at that spot and can no longer be read or copied properly. Bacteria have two systems for dealing with it: one that needs light and one that works in the dark. Sancar worked on both, and humans use the dark one.
Route one: blue light
Photolyase is an enzyme (a protein that speeds up a chemical reaction) that mends the lump with light. In 1958 Rupert showed that visible light can revive bacteria killed by UV, and found the enzyme behind it.
At Chapel Hill Sancar’s group followed photolyase step by step for about 20 years. The enzyme carries two helper molecules: MTHF, an antenna that takes in blue light and passes the energy to FAD, which splits the lump apart. “It is the most beautiful enzyme,” he told UNC in 2025. His lab traced its work down to the picosecond, a millionth of a millionth of a second.
Photolyase is not found in every living thing. For 35 years after its discovery it was an open question whether humans have it. In 1993 his lab published a thorough study that said, plainly, that humans do not have photolyase of either known kind.
Route two, cut and patch
Yale
The dark system is studied in three kinds of UV-sensitive bacteria, each with a broken copy of one gene: uvrA, uvrB or uvrC.
Yale
Sancar clones all three genes and within a few years identifies, isolates and describes the three proteins they code for.
Textbooks
One enzyme cuts the damaged strand on one side of the damage, and a piece of 4 to 6 letters is then eaten away.
Test tube
He puts the purified proteins and damaged DNA together in a test tube. UvrA, UvrB and UvrC make two cuts at once.
Test tube
One cut falls 7 letters to one side of the lump, the other 3 or 4 letters to the other. A piece of 12 or 13 letters, lump included, comes out.
The name
He names the enzyme “ABC excinuclease”, for its unusual two-cut way of working.
The paper
Other groups are racing for the same answer, so he tells only a few colleagues. Dean Rupp presents it in France in spring 1982; the full paper follows in 1983.
Human cells
For five years his lab tries many kinds of cells and tests to catch the piece that human cells cut out, and fails.
Human cells
They catch it: a piece 27 letters long, released by two cuts, in a pattern different from the bacterial one.
Gwen
He later wrote that he told Gwen the result was known only to God and to him.
Students
He told students they had worked day and night for five years; had a group in Japan published a month earlier, those years would have been wasted.
- Transcription-coupled repair
- The enzyme that reads a gene sometimes stalls at damage. Sancar’s lab found a protein, named TRCF, that spots the stalled enzyme, moves it off the damage and helps bring in the cutting enzyme. The finding solved a puzzle that had stood for 30 years. He calls the paper his Yunus Emre Destanı, after the medieval Turkish poet Yunus Emre.
- 1994
- The journal Science names DNA repair its “Molecule of the Year”.
- The checkpoint
- When a cell finds damage it also pauses its division. His lab rebuilt, in a test tube with defined parts, the link between human cut-and-patch repair and this pause, the DNA damage checkpoint.
- The repair map
- After 20 years his lab caught the cut-out piece in living human cells and mapped repair sites across the whole human genome, one letter at a time. The map shows “mountains, valleys and canyons”: places with a lot of repair, an average amount, and little or none. He calls it “My Piri Reis Map”, after the Turkish admiral and mapmaker.
The body clock, and the cryptochromes
The body clock regulates sleep, hormone release, digestion and mood, and disruptions of its timing lead to jet lag. After photolyase, Sancar went looking for its relatives.
Sequences
Human Genome Sciences releases partial sequences of many human genes, and one of them looks like photolyase.
Two genes
Sancar’s lab soon finds a second one. They clone both, and neither protein can repair DNA with light.
Flight
On a flight back from Türkiye he reads a magazine article on the body clock and jet lag. It says blue light sets the clock.
Flight
In some blind mice and people the clock still answers to light, because its own light pathway is separate from the one used for seeing images.
The name
The photolyase-like proteins might be the clock’s blue-light sensors. He suggests the name cryptochrome, with cryptochrome 1 and 2 (CRY1 and CRY2) as the two members.
The paper
The paper comes out. It seems to have escaped the notice of the whole clock research community.
Learning
He sets out to learn the clock and neuroscience from scratch.
Retina and SCN
His lab shows the cryptochrome genes are switched on strongly in the retina and the suprachiasmatic nucleus (SCN), the small part of the brain that keeps the master clock.
PNAS
The CRY1 gene’s message there rises and falls in a daily rhythm. His lab’s PNAS paper proposes that mammalian cryptochromes are clock photoreceptors; he says it electrified the clock field.
- 1998
- A mouse with a changed CRY2 gene, tested in Joseph Takahashi’s lab, is less sensitive to light, and its clock is affected even in complete darkness. Papers on the fruit fly and on the plant Arabidopsis appear within a week. Science names the clock work runner-up for Molecule of the Year.
- 1999
- With colleagues in the United States, Japan and the Netherlands, his lab makes mice that lack both CRY genes. They have no working clock.
- 2000
- By then a detailed model has CRY as the main brake in the clock’s feedback loops. In mammals it does not sense light itself; in fruit flies it is the main light sensor.
The loop, simplified
- Genes switch on. Clock genes are read, and clock proteins start to pile up.
- Proteins build up. CRY is one of them.
- The brake goes on. CRY switches the clock genes off again.
- The proteins break down. The brake lets go, and the cycle starts again, about every 24 hours.
Full circle
Sancar’s lab then found that the clock steers excision repair in mice, and that the cancer-causing effect of UV light follows a daily pattern. “They all link together,” he says: the bacterial protein photolyase is related to the clock protein cryptochrome, and cryptochrome regulates nucleotide excision repair.
Stockholm and Ankara, 2015 and 2016
- 7 October 2015
- The Royal Swedish Academy of Sciences announces the 2015 Chemistry prize. TÜBA, the Turkish Academy of Sciences, of which he is an honorary member, calls him the first Turkish scientist to win it.
- 8 December 2015
- Sancar gives his Nobel lecture, “Mechanisms of DNA Repair by Photolyase and Excision Nuclease”, at the Aula Magna of Stockholm University. The chair of the Nobel Committee for Chemistry introduces him.
- 10 December 2015
- He receives the prize from King Carl XVI Gustaf at the award ceremony. The head of TÜBİTAK, the Turkish science council, is in the hall. His diploma is a work of art by Ingela Berntsson with lettering by Annika Rücker.
- 15 December 2015
- In Ankara he visits the Atatürk Mausoleum, Anıtkabir. That week a dinner in his honour is given at the Presidential Complex, with Gwen Sancar at his side.
- 19 May 2016
- He gives the medal and the certificate of his Nobel Prize to the Anıtkabir Command in a ceremony at Anıtkabir. Gwen Sancar is there too.
“By giving this medal here, I have paid my debt of loyalty to Atatürk and to his comrades, the founders of the Republic of Türkiye.”
Sancar, at the ceremony of 19 May 2016.
At TEKNOFEST, 27 September 2021
He was the guest of honour of TÜBİTAK at TEKNOFEST, the aviation, space and technology festival, and his first stop was the TÜBİTAK Science High School in Gebze. He lectured the students and answered their questions. Asked how he applied for the Nobel Prize, he said that nobody can: you cannot nominate yourself, and he still does not know who nominated him. Turkish schools, he told them, had prepared him well in theory but not in experiments, and science is done through experiments.
Chapel Hill and home
Sancar is the Sarah Graham Kenan Professor of Biochemistry and Biophysics at the University of North Carolina at Chapel Hill, where he has worked since 1982. In October 2025, aged 79, he was still teaching an advanced molecular biology course (BIOC 631) every spring and supervising undergraduate research.
Over 40 years he has trained more than 35 students and 55 postdoctoral researchers, and, UNC says, his lab’s most recent work is a new biochemical approach to treating brain tumours.
His advice to young scientists, as UNC reports it
- Choose well. Pick a topic that will make a difference.
- Work very hard. Only about one experiment in five works.
- Read the journals the day they come out. That habit paid off for him: he could purify large amounts of photolyase only because he had seen a paper in Nature about cloning genes.
He gives the credit for the lab’s results to its students and postdocs.
Chapel Hill also has a Turkish house
- 2007
- He and Gwen found the Aziz and Gwen Sancar Foundation, which aims to advance education and understanding between the United States and Türkiye.
- The centre
- The foundation runs the Sancar Turkish Cultural and Community Center at 1609 E. Franklin Street, which offers Turkish cooking classes, history lessons and cultural events.
- August 2023
- The couple begin building the Sancar Scholars Residence behind it, a home for eight to ten Turkish scholars who visit or study at UNC.
The museum in Savur
On 21 October 2026 the Aziz Sancar Museum opened in Savur, in the house where he was born, grew up and stayed while he practised medicine. It fills one floor, 395 square metres, of a four-storey stone building in the Sefa neighbourhood. Its three halls show photographs, medical instruments, diplomas, gowns, gifts, awards and files on his research. The basement and the other floors are to become a reading room and a science centre, run by the Mardin governorship.
Quick answers, and the sources
Who is Aziz Sancar?
A biochemist and doctor from Savur, in Mardin province, who shared the 2015 Nobel Prize in Chemistry. He teaches at the University of North Carolina at Chapel Hill.
Where was Aziz Sancar born?
In Savur, a town in Mardin province in south-eastern Türkiye, on 8 September 1946. He was the seventh of eight children.
How old is Aziz Sancar?
He was born on 8 September 1946, so he turned 80 in September 2026.
What did Aziz Sancar win the Nobel Prize for?
For mapping nucleotide excision repair, the way cells cut a stretch of UV-damaged DNA out and patch the gap. He shared the prize with Tomas Lindahl and Paul Modrich, one third each.
Who shared the 2015 Nobel Prize in Chemistry with him?
Tomas Lindahl, who found how cells swap out single damaged letters, and Paul Modrich, who showed how cells correct copying mistakes.
What is DNA repair in simple words?
Cells copy their DNA millions of times a day and damage it all the time. Teams of proteins find the damaged spot, cut it out and refill it. Sancar showed how two routes work: blue light with the enzyme photolyase, and cut and patch.
What is photolyase?
An enzyme that mends UV damage with blue light. Claud Rupert found it in 1958, and Sancar cloned its gene in 1975 and traced how it works. Humans do not have it.
What is nucleotide excision repair?
The cut-and-patch route. Proteins find a damaged spot, cut the strand twice, take out a short piece with the damage in it and fill the gap with new letters. In bacteria the piece is 12 or 13 letters long, in human cells 27.
What are cryptochromes?
Light-sensing proteins that look like photolyase but do not repair DNA. Sancar suggested the name in 1996. They help run the 24-hour body clock, and mice that lack both of them have no working clock.
Who is Gwen Sancar?
His wife and a fellow scientist. Gwen Boles met him as a graduate student in Dallas, and they married in 1978. She is a professor of biochemistry and biophysics.
Where are his Nobel medal and certificate?
At Anıtkabir in Ankara. He gave them to the Anıtkabir Command on 19 May 2016.
Is Aziz Sancar still working?
Yes. In October 2025, aged 79, he still taught a course and ran his lab at UNC.
Was he the first Turkish winner of the Nobel Prize in Chemistry?
Yes. He holds both Turkish and US citizenship.
Is there an Aziz Sancar museum?
Yes. It opened on 21 October 2026 in his family house in Savur.
Read the sources
- Aziz Sancar: Biographical (his own account, written for the Nobel Prize) — Nobel Prize Outreach, checked 23 October 2026
- Press release: The Nobel Prize in Chemistry 2015, 7 October 2015 — The Royal Swedish Academy of Sciences, checked 23 October 2026
- The Nobel Prize in Chemistry 2015: Popular information — The Royal Swedish Academy of Sciences, checked 23 October 2026
- The Nobel Prize in Chemistry 2015: Award ceremony speech, 10 December 2015 — Nobel Prize Outreach, checked 23 October 2026
- Aziz Sancar: Facts — Nobel Prize Outreach, checked 23 October 2026
- Aziz Sancar: Nobel diploma — Nobel Prize Outreach, checked 23 October 2026
- Aziz Sancar: Nobel Lecture, 8 December 2015 — Nobel Prize Outreach, checked 23 October 2026
- Gurur Günü: Prof. Dr. Aziz Sancar Ödülünü Aldı (news, 11 December 2015) — TÜBİTAK, the Scientific and Technological Research Council of Türkiye, checked 23 October 2026
- Cumhurbaşkanı Erdoğan, Nobel Kimya Ödülü Sahibi Prof. Dr. Sancar’ı Kabul Etti (news, 16 December 2015) — TÜBİTAK, the Scientific and Technological Research Council of Türkiye, checked 23 October 2026
- TÜBA Şeref Üyesi Prof. Dr. Aziz Sancar 2015 Nobel Kimya Ödülü’nü Kazandı (news, 7 October 2015) — TÜBA, the Turkish Academy of Sciences, checked 23 October 2026
- Nobel Ödülü’nün Anıtkabir Komutanlığına Takdim Töreni (news, 19 May 2016) — The Presidency of the Republic of Türkiye, checked 23 October 2026
- TUBITAK’s Guest of Honor Prof. Dr. Aziz Sancar’s First Stop was TUBITAK Science High School in Gebze (news, 27 September 2021) — TÜBİTAK Marmara Research Center, checked 23 October 2026
- The enduring legacy of Dr. Aziz Sancar (7 October 2025) — University of North Carolina at Chapel Hill, UNC Giving, checked 23 October 2026
- Mardin Savur’da “Aziz Sancar Müzesi” ziyarete açıldı (news, 21 October 2026) — Anadolu Agency, checked 23 October 2026