Aziz Sancar, M.D., Ph.D.

Research: DNA damage repair, cell cycle checkpoints, circadian clock, and the coupling of these processes in organisms ranging from E. coli to mice to human cells

Sarah Graham Kenan Professor of Biochemistry and Biophysics
Adjunct Appointment in Biology
(PhD – University of Texas; MD – Istanbul University)



  • 1969 MD, Summa Cum Laude (1st in class of 625)
  • 1977 PhD, University of Texas at Dallas
  • 1984 NSF Presidential Young Investigator Award
  • 1995 NIH MERIT Award
  • 2004 American Academy of Arts and Sciences
  • 2005 National Academy of Sciences, USA
  • 2006 Turkish Academy of Sciences
  • 2007 Turkish Koç Award
  • 2009 Univ. of Texas at Dallas Distinguished Alumni Award
  • 2014 Distinguished Visiting Professor – Academia Sinica
  • 2015 Nobel Prize in Chemistry
  • 2016 TWESCO International Turkish Academy – Gold Medal at UN
  • 2016 ASBMB American Society for Biochemistry & Molecular Biology – Bert and Natalie Vallee Award
  • 2016 O. Max Gardner Award – highest honor by UNC Board of Governors
  • 2016 Carnegie Corporation’s Immigrant of the Year
  • 2016 North Carolina Award – the highest civilian honor given by the state
  • 2016 National Academy of Medicine
  • In addition, many awards and honorary doctorate degrees


Our lab works on three interrelated subjects: (1) Mammalian DNA Excision Repair; (2) Mammalian DNA Damage Checkpoints; (3) Mammalian Circadian Clock. Although all three systems mediate organismal response to external and internal signals so as to maintain homeostasis and adaptation to the environment by different mechanisms, they are at the organism level, coupled systems.

Fig 1
Fig. 1. The XR-seq method. (A) Schematic of nucleotide excision repair. (B) Excision patterns of photoproducts in wild-type, XP-C (deficient in global re-pair), and CS-B (deficient in TCR) cells. (C) Procedure for preparation of the dsDNA library for the Illumina HiSeq 2000 platform. (D) Distribution of the XR-seq signal, separated by strand, for CPD (top) and (6-4)PP (bot-tom) over a 1.5-Mb region of chromosome 3. (E) Strong association of TCR with RNA levels.

DNA Repair

DNA damage by exogenous physical and chemical agents is the most common cause of cancer. Conversely, some of the most commonly used anticancer drugs kill malignant cells by damaging their DNA. DNA Repair is the ensemble of molecular mechanisms that eliminate DNA damage from the genome, and it plays crucial roles in carcinogenesis and in cancer therapy. Our lab works on Nucleotide Excision Repair which is the sole pathway for repairing cyclobutane pyrimidine dimers (CPDs) and cisplatin 1,2-d(GpG) adducts that cause cancer and cure cancer, respectively. We discovered that these lesions are removed from DNA by dual incisions that generate 24-32 nucleotide-long oligomers (“nominal 30-mer”). We identified and purified the 6 repair factors, RPA, XPA, XPC, TFIIH, XPG, XPF-ERCC1, that are essential for dual incisions. Using these purified factors, we reconstituted human excision repair in vitro and defined the molecular mechanism of excision repair. The in vitro work was complemented by in vivo studies which enabled us to generate a repair map of the entire genome. We discovered that the nominal 30-mer is released in a tight complex with TFIIH, and this finding enabled us to isolate the nominal 30-mers from irradiated cells and subject them to deep sequencing (Fig. 1). By using normal human fibroblasts and mutant cell lines we created repair maps for general repair and transcription-coupled repair of UV damage for the entire human genome through this method which we have named XR-seq (eXcision Repair-Sequencing). Our future work will exploit XR-seq to uncover novel genomic regulators of excision repair of DNA damage by anti-cancer drugs with the ultimate goal of developing improved chemotherapy regimens. In addition, we plan to investigate the effect of the excised nominal 30-mer on cellular physiology and the processing and ultimate fates of the excised oligonucleotides.

DNA Damage Checkpoints

Fig 2
Fig. 2. (A) Coupling Excision Repair and the ATR-mediated Checkpoint. When DNA is damaged by UV or a UV-mimetic agent, the core excision repair factors (RPA, XPA, XPC, TFIIH, XPG, XPF-ERCC1) excise a ∼30-nt oligomer containing the damage. The resulting gap is either filled in by polymerases or the gap is enlarged by EXO1. The enlarged ssDNA gap is coated with RPA, which recruits ATR-ATRIP, TopBP1, and substrates including p53. (B) Schematic of repair-checkpoint coupling in vitro. (C) Repair-checkpoint coupling Kinase reactions containing RPA as a substrate were incubated with ATR-ATRIP, TopBP1, and EXO1 as indicated. Kinase reactions containing unmodified (UM) or AAF-DNA from excision reactions with or without repair factors (RF) as indicated. Reactions were analyzed by immune-blotting for phospho-RPA2 (Ser33).

DNA Damage Checkpoints are intracellular signaling pathways that delay or arrest cell cycle progression in response to DNA damage and thus aid in preventing mutations and cellular and organismic death. In human cells, two main DNA damage checkpoints pathways have been defined that are governed by the ATM and ATR protein kinases. The ATR pathway is activated by UV or by replication block by base damage or by nucleotide depletion. In line with our interest with cellular response to UV and UV-mimetic agents, we have been studying the ATR-mediated DNA damage checkpoint response using in vitro systems with purified proteins as well as cell-based assays. Using purified proteins and model DNA substrates that mimic the initiating triggers for DNA damage checkpoint activation, we have reconstituted the bases ATR-dependent signaling reaction. Importantly, we have succeeded in linking DNA excision repair to the ATR checkpoint pathway (Fig. 2): Using purified core nucleotide excision repair factors (RPA, XPA, XPC, TFIIH, XPG, and XPF-ERCC1), core DNA damage checkpoint proteins (ATR-ATRIP, TopBP1, RPA), and damaged DNA, we coupled excision repair to the ATR-mediated checkpoint. We found that checkpoint signaling as measured by phosphorylation of target proteins (RPA, p53) required the enlargement of the single-strand gap generated by the excision repair system by the 5’ to 3’ exonuclease activity of EXO1 enzyme in accordance with the in vivo data. Future work will take advantage of our unique in vitro system to characterize novel regulators of ATR signaling and to screen and validate promising anti-cancer drugs that inhibit the ATR function.

Cryptochrome and the Circadian Clock

Fig 3
Fig. 3. Current Model for the Mammalian Circadian Clock. (A) Mammalian molecular clock model of the transcription-translation feedback loop (TTFL). (B) PER2 removes CRY1 from the CRY1:CLOCK:BMAL1:E-box complex. (C) New model for the mammalian circadian clock. The figure shows a semiquantitative heat map representation of CRY1 and PER2 protein expression as well as the ChIP data for CLOCK:BMAL1 and CRY1 over a circadian cycle and its consequences with regard to interactions of core clock proteins with the E-box and the effects of these interactions on transcription of genes (Nr1d1 and Dbp) regulated exclusively by the core TTFL.

The circadian clock is the internal timekeeping system that controls cyclic changes in physiology and behavior to prepare the organism for the unique challenges of the solar day. In mice and humans the circadian rhythm at the organismal level is generated by a molecular clock of periodicity of ~24 hrs. The molecular clock consists of a transcription-translation feedback loop (TTFL) in which the heterodimeric transcriptional activator CLOCK-BMAL1 promotes transcription of transcriptional repressors, CRY (Cryptochrome) and PER (Period) which counter the activity of CLOCK-BMAL1 as shown in Fig. 3A. Our group discovered that CRY is a core human clock protein and that it mediates repression by two mechanisms (Fig. 3B,C): In one CRY binds to the CLOCK-BMAL1 complex on DNA and blocks its interaction with the transcription machinery. In the second mode of repression, the co-repressor PER displaces the entire activator complex from the promoter in a CRY-dependent manner. Our research has provided a mechanistic basic for how this dual repression mechanism confers precision and resilience and, at the same time, flexibility and adaptability to the signaling pathways and networks and therefore influences physio-pathologic conditions ranging from sleep regulation and jetlag to metabolic syndrome to cancer. We discovered that the circadian clock regulates nucleotide excision repair and hence the susceptibility to UV-induced skin cancer as a function of time of the day of exposure to light. Because excision repair is also the main repair mechanism for removing DNA lesions from the genome that are generated by the anti-cancer drug cisplatin, we are currently working at translating our finding of clock-excision repair connection to develop improved chemotherapy regimens.

RECENT PUBLICATIONS (Click for full publication list)

  • Li W, Liu W, Kakoki A, Wang R, Adebali O, Jiang Y, Sancar A. (2019) Nucleotide excision repair capacity increases during differentiation of human embryonic carcinoma cells into neurons and muscle cells. J Biol Chem. 294(15):5914-5922. PMID: 30808711.
  • Yimit A, Adebali O, Sancar A, Jiang Y (2019) Differential damage and repair of DNA-adducts induced by anti-cancer drug cisplatin across mouse organs. Nature Communications 10(1), 309.
  • Hu J, Li W, Adebali O, Yang Y, Oztas O, Selby CP, Sancar A. (2019) Genome-wide mapping of nucleotide excision repair with XR-seq. Nature Protocols 14(1):248-282. PMID: 30552409.
  • Yang Y, Hu J, Selby CP, Li W, Yimit A, Jiang Y, Sancar A. (2019) Single-nucleotide resolution analysis of nucleotide excision repair of ribosomal DNA in humans and mice. J Biol Chem. 294(1):210-217. doi: 10.1074/jbc.RA118.006121. PMID: 30413533.
  • Wang X, Jing C, Selby CP, Chiou YY, Yang Y, Wu W, Sancar A, Wang J. (2018) Comparative properties and functions of type 2 and type 4 pigeon cryptochromes. Cell Mol Life Sci.  75(24):4629-4641. doi: 10.1007/s00018-018-2920-y. PMID: 30264181.
  • Yang Y, Adebali O, Wu G, Selby CP, Chiou YY, Rashid N, Hu J, Hogenesch JB, Sancar A. (2018) Cisplatin-DNA adduct repair of transcribed genes is controlled by two circadian programs in mouse tissues. Proceedings of the National Academy of Sciences of the United States of America 115(21):E4777-E4785. PMID: 30413533.
  • Li W, Adebali O, Yang Y, Selby CP, Sancar A (2018) Single-nucleotide resolution dynamic repair maps of UV damage in Saccharomyces cerevisiae genome. Proceedings of the National Academy of Sciences of the United States of America 115(15):E3408-E3415.
  • Oztas O, Selby CP, Sancar A, Adebali O. (2018) Genome-wide excision repair in Arabidopsis is coupled to transcription and reflects circadian gene expression patterns. Nature Communications 9(1):1503. doi: 10.1038/s41467-018-03922-5. PMID: 29666379.
  • Chiou YY, Hu J, Sancar A, Selby CP. (2017) RNA polymerase II is released from the DNA template during transcription-coupled repair in mammalian cells. J Biol Chem. pii: jbc.RA117.000971. doi: 10.1074/jbc.RA117.000971. [Epub ahead of print] PMID: 29282293.
  • Hughes ME, Abruzzi KC, Allada R, Anafi R, Arpat AB, Asher G, Baldi P, de Bekker C, Bell-Pedersen D, Blau J, Brown S, Ceriani MF, Chen Z, Chiu JC, Cox J, Crowell AM, DeBruyne JP, Dijk DJ, DiTacchio L, Doyle FJ, Duffield GE, Dunlap JC, Eckel-Mahan K, Esser KA, FitzGerald GA, Forger DB, Francey LJ, Fu YH, Gachon F, Gatfield D, de Goede P, Golden SS, Green C, Harer J, Harmer S, Haspel J, Hastings MH, Herzel H, Herzog ED, Hoffmann C, Hong C, Hughey JJ, Hurley JM, de la Iglesia HO, Johnson C, Kay SA, Koike N, Kornacker K, Kramer A, Lamia K, Leise T, Lewis SA, Li J, Li X, Liu AC, Loros JJ, Martino TA, Menet JS, Merrow M, Millar AJ, Mockler T, Naef F, Nagoshi E, Nitabach MN, Olmedo M, Nusinow DA, Ptáček LJ, Rand D, Reddy AB, Robles MS, Roenneberg T, Rosbash M, Ruben MD, Rund SSC, Sancar A, Sassone-Corsi P, Sehgal A, Sherrill-Mix S, Skene DJ, Storch KF, Takahashi JS, Ueda HR, Wang H, Weitz C, Westermark PO, Wijnen H, Xu Y, Wu G, Yoo SH, Young M, Zhang EE, Zielinski T, Hogenesch JB (2017) Guidelines for Genome-Scale Analysis of Biological Rhythms. Journal of biological rhythms 32(5), 380-393.
  • Adebali O, Sancar A, Selby CP (2017) Mfd translocase is necessary and sufficient for transcription-coupled repair in Escherichia coli.
    The Journal of biological chemistry 292(45), 18386-18391.
  • Hu J, Selby CP, Adar S, Adebali O, Sancar A. (2017) Molecular mechanisms and genomic maps of DNA excision repair in E.coli and humans. J Biol Chem.R117.807453. doi: 10.1074/jbc.R117.807453. (in press).
  • Hu J, Adebali O, Adar S, Sancar A. (2017) Dynamic maps of UV damage formation and repair for the human genome. Proc Natl Acad Sci U S A. 114(26):6758-6763. doi: 10.1073/pnas.1706522114.
  • Li W, Hu J, Adebali O, Adar S, Yang Y, Chiou YY, Sancar A. (2017) Human genome-wide repair map of DNA damage caused by the cigarette smoke carcinogen benzo[a]pyrene. Proc Natl Acad Sci U S A. 114(26):6752-6757. doi: 10.1073/pnas.1706021114. PMID: 28607059.
  • Li W, Hu J, Adebali O, Adar S, Yang Y, Chiou YY, Sancar A. (2017) Human genome-wide repair map of DNA damage caused by the cigarette smoke carcinogen benzo[a]pyrene. Proc Natl Acad Sci U S A. 114(26):6752-6757. doi: 10.1073/pnas.1706021114.
  • Krishnaiah SY, Wu G, Altman BJ, Growe J, Rhoades SD, Coldren F, Venkataraman A, Olarerin-George AO, Francey LJ, Mukherjee S, Girish S, Selby CP, Cal S, Er U, Sianati B, Sengupta A, Anafi RC, Kavakli IH, Sancar A, Baur JA, Dang CV, Hogenesch JB, Weljie AM. (2017) Clock Regulation of Metabolites Reveals Coupling between Transcription and Metabolism. Cell Metab. 4;25(4):961-974.e4. doi: 10.1016/j.cmet.2017.03.019.
  • Adebali, O, Chiou YY, Hu J, Sancar A, Selby CP. (2017) Genome-wide transcription-coupled repair in Escherichia coli is mediated by the Mfd translocase. Proc Natl Acad Sci U S A. 14;114(11):2116-2125. PMID: 28167766.Zhang M, Wang L, Shu S, Sancar A, Zhong D. (2016) Bifurcating electron-transfer pathways in DNA photolyases determine the repair quantum yield. Science. 14;354(6309):209-213.
  • Zhang M, Wang L, Shu S, Sancar A, Zhong D. (2016) Bifurcating electron-transfer pathways in DNA photolyases determine the repair quantum yield. Science.  354(6309):209-213. PMID: 27738168.
  • Hu J, Lieb JD, Sancar A, Adar S. (2016) Cisplatin DNA damage and repair maps of the human genome at single-nucleotide resolution. Proc Natl Acad Sci U S A. 11;113(41):11507-11512.
  • Chiou YY, Yang Y, Rashid N, Ye R, Selby CP, Sancar A. (2016) Mammalian Period represses and de-represses transcription by displacing CLOCK-BMAL1 from promoters in a Cryptochrome-dependent manner. Proc Natl Acad Sci U S A. 11;113(41):E6072-E6079.
  • Sancar A. (2016) Mechanisms of DNA Repair by Photolyase and Excision Nuclease (Nobel Lecture). Angew Chem Int Ed Engl. 18;55(30):8502-27. doi: 10.1002/anie.201601524.
  • Jang H, Lee GY, Selby C, Lee G, Jeon YG, Lee JH, Cheng KKY, Titchenell P, Birnbaum M, Xu A, Sancar A, Kim JB. (2016) SREBP1c-CRY1 signaling represses hepatic glucose production by promoting FOXO1 degradation during refeeding. Nat Commun.
  • Lindahl T, Modrich P, Sancar A. (2016) The 2015 Nobel Prize in Chemistry The Discovery of Essential Mechanisms that Repair DNA Damage. J Assoc Genet Technol.  42(1):37-41. PMID: 27183258.
  • Canturk F, Karaman M, Selby CP, Kemp MG, Kulaksiz-Erkmen G, Hu J, Li W, Lindsey-Boltz LA, Sancar A. (2016) Nucleotide excision repair by dual incisions in plants. Proc Natl Acad Sci U S A.
  • Adar S, Hu J, Lieb JD, Sancar A. (2016) Genome-wide kinetics of DNA excision repair in relation to chromatin state and mutagenesis. Proc Natl Acad Sci U S A. 113(15):E2124-33.
  • Kemp MG, Sancar A. (2016) ATR Kinase Inhibition Protects Non-cycling Cells from the Lethal Effects of DNA Damage and Transcription Stress. J Biol Chem. (17):9330-42.
  • Lindsey-Boltz LA, Kemp MG, Hu J, Sancar A. (2015) Analysis of ribonucleotide removal from DNA by human nucleotide excision repair. J Biol Chem. 290(50):29801-7.
  • Choi JH, Kim SY, Kim SK, Kemp MG, Sancar A. (2015) An Integrated Approach for Analysis of the DNA Damage Response in Mammalian Cells: Nucleotide Excision Repair, DNA Damage Checkpoint, and Apoptosis. J Biol Chem. 290(48):28812:21.
  • Tan C, Liu Z, Li J, Guo X, Wang L, Sancar A, Zhong D. (2015) The molecular origin of high DNA-repair efficiency by photolyase. Nat Commun. 6:7302.
  • Hu J, Adar S, Selby CP, Lieb JD, Sancar A. (2015) Genome-wide analysis of human global and transcription-coupled excision repair of UV damage at single-nucleotide resolution. Genes Dev. 29(9):948-60.
  • Kemp MG, Lindsey-Boltz LA, Sancar A. (2015) UV light potentiates STING (stimulator of interferon genes)-dependent innate immune signaling through deregulation of ULK1 (Unc51-like kinase 1). J Biol Chem. 290(19):12184-94.
  • Lindsey-Boltz LA, Kemp MG, Capp C, Sancar A. (2015) RHINO forms a stoichiometric complex with the 9-1-1 checkpoint clamp and mediates ATR-Chk1 signaling. Cell Cycle 14(1):99-108.
  • Gaddameedhi S, Selby CP, Kemp MG, Ye R, Sancar A. (2014) The Circadian Clock Controls Sunburn Apoptosis and Erythema in Mouse Skin. J Invest Dermatol. 135(4):1119-27.
  • Sancar A, Lindsey-Boltz LA, Gaddameedhi S, Selby CP, Ye R, Chiou Y-Y, Kemp MG, Hu J, Lee JH, Ozturk N. (2015) Circadian Clock, Cancer, and Chemotherapy. Biochemistry 54(2):110-23.
  • Ye R, Selby CP, Chiou YY, Ozkan-Dagliyan I, Gaddameedhi S, Sancar A. (2014) Dual modes of CLOCK:BMAL1 inhibition mediated by Cryptochrome and Period proteins in the mammalian circadian clock. Genes Dev. 28(18):1989-98.
  • Kemp MG, Gaddameedhi S, Choi JH, Hu J, Sancar A. (2014) DNA repair synthesis and ligation affect the processing of excised oligonucleotides generated by human nucleotide excision repair. J Biol Chem. 289(38):26574-83.
  • Tan C, Guo L, Ai Y, Li J, Wang L, Sancar A, Luo Y, Zhong D. (2014) Direct Determination of Resonance Energy Transfer in Photolyase: Structural Alignment for the Functional State. J Phys Chem A. 118(45):10522-30.
  • Ozturk N, Selby CP, Zhong D, Sancar A. (2014) Mechanism of Photosignaling by Drosophila Cryptochrome:Role of the Redox Status of the Flavin Chromophore. J Biol Chem. 289: 4634-4642.
  • Annayev Y, Adar S, Chiou YY, Lieb J, Sancar A, Ye R. (2014) Gene Model 129 (Gm129) Encodes a Novel Transcriptional Repressor that Modulates Circadian Gene Expression. J Biol Chem. 289: 5013-5024.
  • Lindsey-Boltz LA, Kemp MG, Reardon JT, Derocco V, Iyer RR, Modrich P, Sancar A. (2014) Coupling of Human DNA Excision Repair and ATR-mediated DNA Damage Checkpoint in a Defined In Vitro System. J Biol Chem. 289: 5074-5082.
  • Choi JH, Gaddameedhi S, Kim SY, Hu J, Kemp MG, Sancar A. (2014) Highly specific and sensitive method for measuring nucleotide excision repair kinetics of ultraviolet photoproducts in human cells. Nucleic Acids Res. 42(4):e29.
  • Liu Z, Tan C, Guo X, Li J, Wang L, Sancar A, Zhong D. (2013) Determining complete electron flow in the cofactor photoreduction of oxidized photolyase. Proc Natl Acad Sci U S A 110(32):12966-71.
  • Liu Z, Zhang M, Guo X, Tan C, Li J, Wang L, Sancar A, Zhong D. (2013) Dynamic determination of the functional state in photolyase and the implication for cryptochrome. Proc Natl Acad Sci U S A 110(32):12972-7.
  • Ozkan-Dagliyan I, Chiou YY, Ye R, Hassan BH, Ozturk N, Sancar A. (2013) Formation of Arabidopsis Cryptochrome 2 Photobodies in Mammalian Nuclei: Application as an Optogenetic DNA Damage Checkpoint Switch. J Biol Chem. 288(32):23244-51.
  • Hu J, Choi JH, Gaddameedhi S, Kemp MG, Reardon JT, Sancar A. (2013) Nucleotide Excision Repair in Human Cells: Fate of the Excised Oligonucleotide Carrying DNA Damage In Vivo. J Biol Chem. 288(29):20918-26.
  • Hassan BH, Lindsey-Boltz LA, Kemp MG, Sancar A. (2013) Direct role for the replication protein Treslin (Ticrr) in the ATR-mediated checkpoint response. J Biol Chem. 288(26):18903-10.
  • Ozturk N, VanVickle-Chavez SJ, Akileswaran L, Van Gelder RN, Sancar A. (2013) Ramshackle (Brwd3) promotes light-induced ubiquitylation of Drosophila Cryptochrome by DDB1-CUL4-ROC1 E3 ligase complex. Proc Natl Acad Sci U S A 110(13):4980-5.
  • Lee JH, Gaddameedhi S, Ozturk N, Ye R, Sancar A. (2013) DNA Damage-Specific Control of Cell Death by Cryptochrome in p53-Mutant Ras-Transformed Cells. Cancer Res. 73(2):785-91.

Lab Contact:

Lab Rooms: 3077 Genetic Medicine Building
Lab Phone: 919-962-0115