pyrimidine dimers


Summary: Dimers found in DNA chains damaged by ULTRAVIOLET RAYS. They consist of two adjacent PYRIMIDINE NUCLEOTIDES, usually THYMINE nucleotides, in which the pyrimidine residues are covalently joined by a cyclobutane ring. These dimers block DNA REPLICATION.

Top Publications

  1. Hidema J, Taguchi T, Ono T, Teranishi M, Yamamoto K, Kumagai T. Increase in CPD photolyase activity functions effectively to prevent growth inhibition caused by UVB radiation. Plant J. 2007;50:70-9 pubmed
    ..However, further protection from UVB-induced damage may require the genetic enhancement of other systems as well. ..
  2. Sugasawa K, Okuda Y, Saijo M, Nishi R, Matsuda N, Chu G, et al. UV-induced ubiquitylation of XPC protein mediated by UV-DDB-ubiquitin ligase complex. Cell. 2005;121:387-400 pubmed
    ..Our results strongly suggest that ubiquitylation plays a critical role in the transfer of the UV-induced lesion from UV-DDB to XPC. ..
  3. Thorne R, Chinnapen D, Sekhon G, Sen D. A deoxyribozyme, Sero1C, uses light and serotonin to repair diverse pyrimidine dimers in DNA. J Mol Biol. 2009;388:21-9 pubmed publisher
  4. Pines A, Backendorf C, Alekseev S, Jansen J, de Gruijl F, Vrieling H, et al. Differential activity of UV-DDB in mouse keratinocytes and fibroblasts: impact on DNA repair and UV-induced skin cancer. DNA Repair (Amst). 2009;8:153-61 pubmed publisher
    ..protein (UV-DDB) is essential for global genome nucleotide excision repair of UV-induced cyclobutane pyrimidine dimers (CPD) and accelerates repair of 6-4 photoproducts (6-4PP)...
  5. de Lima Bessa K, Armelini M, Chiganças V, Jacysyn J, Amarante Mendes G, Sarasin A, et al. CPDs and 6-4PPs play different roles in UV-induced cell death in normal and NER-deficient human cells. DNA Repair (Amst). 2008;7:303-12 pubmed
    Ultraviolet (UV) light generates two major DNA lesions: cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6-4)-pyrimidone photoproducts (6-4PPs), but the specific participation of these two lesions in the deleterious effects of UV is ..
  6. Narbutt J, Lesiak A, Jochymski C, Kozlowski W, Sysa Jedrzejowska A, Norval M. Increased cyclooxygenase expression and thymine dimer formation after repeated exposures of humans to low doses of solar simulated radiation. Exp Dermatol. 2007;16:837-43 pubmed
    ..In contrast, for dTT formation, the repeated SSR exposures led to a limited degree of both photoadaptation and photoprotection. ..
  7. Kwon Y, Smerdon M. DNA repair in a protein-DNA complex: searching for the key to get in. Mutat Res. 2005;577:118-30 pubmed
    ..and the 5S ribosomal RNA gene (5S rDNA), we previously measured position-dependent effects of cyclobutane pyrimidine dimers (CPDs) at five different sites within the internal control region (ICR) on complex formation [Y. Kwon, M.J...
  8. Hu J, Choi J, Gaddameedhi S, Kemp M, Reardon J, Sancar A. Nucleotide excision repair in human cells: fate of the excised oligonucleotide carrying DNA damage in vivo. J Biol Chem. 2013;288:20918-26 pubmed publisher
    ..Taken together, our results show the congruence of in vivo and in vitro data on nucleotide excision repair in humans. ..
  9. Nguyen K, Burrows C. A prebiotic role for 8-oxoguanosine as a flavin mimic in pyrimidine dimer photorepair. J Am Chem Soc. 2011;133:14586-9 pubmed publisher
    ..This unusual example of one form of DNA damage, oxidation, functioning to repair another, photodimerization, may provide insight into the origins of prebiotic redox processes. ..

More Information


  1. Palomera Sanchez Z, Zurita M. Open, repair and close again: chromatin dynamics and the response to UV-induced DNA damage. DNA Repair (Amst). 2011;10:119-25 pubmed publisher
  2. Cannistraro V, Taylor J. Acceleration of 5-methylcytosine deamination in cyclobutane dimers by G and its implications for UV-induced C-to-T mutation hotspots. J Mol Biol. 2009;392:1145-57 pubmed publisher tumor suppressor genes and are thought to arise from translesion synthesis past deaminated cyclobutane pyrimidine dimers (CPDs)...
  3. Jansen J, Tsaalbi Shtylik A, Hendriks G, Gali H, Hendel A, Johansson F, et al. Separate domains of Rev1 mediate two modes of DNA damage bypass in mammalian cells. Mol Cell Biol. 2009;29:3113-23 pubmed publisher
    ..These gaps are inducers of DNA damage signaling leading to an irreversible G(2) arrest. Our results corroborate a model in which Rev1-mediated DNA damage bypass at postreplicative gaps quenches irreversible DNA damage responses. ..
  4. Ikehata H, Kawai K, Komura J, Sakatsume K, Wang L, Imai M, et al. UVA1 genotoxicity is mediated not by oxidative damage but by cyclobutane pyrimidine dimers in normal mouse skin. J Invest Dermatol. 2008;128:2289-96 pubmed publisher
    UVA1 induces the formation of 8-hydroxy-2'-deoxyguanosines (8-OH-dGs) and cyclobutane pyrimidine dimers (CPDs) in the cellular genome...
  5. Schreier W, Schrader T, Koller F, Gilch P, Crespo Hernandez C, Swaminathan V, et al. Thymine dimerization in DNA is an ultrafast photoreaction. Science. 2007;315:625-9 pubmed
    ..The low quantum yield of this photoreaction is proposed to result from infrequent conformational states in the unexcited polymer, revealing a strong link between conformation before light absorption and photodamage. ..
  6. Yoon J, Prakash L, Prakash S. Highly error-free role of DNA polymerase eta in the replicative bypass of UV-induced pyrimidine dimers in mouse and human cells. Proc Natl Acad Sci U S A. 2009;106:18219-24 pubmed publisher
    Cyclobutane pyrimidine dimers (CPDs) constitute the most frequent UV-induced DNA photoproduct...
  7. Mouret S, Philippe C, Gracia Chantegrel J, Banyasz A, Karpati S, Markovitsi D, et al. UVA-induced cyclobutane pyrimidine dimers in DNA: a direct photochemical mechanism?. Org Biomol Chem. 2010;8:1706-11 pubmed publisher
    ..Yet, it was recently shown that cyclobutane pyrimidine dimers (CPD), well known for their involvement in UVB genotoxicity, are produced in larger yield than oxidative ..
  8. Hendel A, Ziv O, Gueranger Q, Geacintov N, Livneh Z. Reduced efficiency and increased mutagenicity of translesion DNA synthesis across a TT cyclobutane pyrimidine dimer, but not a TT 6-4 photoproduct, in human cells lacking DNA polymerase eta. DNA Repair (Amst). 2008;7:1636-46 pubmed publisher
  9. Wittschieben B, Iwai S, Wood R. DDB1-DDB2 (xeroderma pigmentosum group E) protein complex recognizes a cyclobutane pyrimidine dimer, mismatches, apurinic/apyrimidinic sites, and compound lesions in DNA. J Biol Chem. 2005;280:39982-9 pubmed
    ..Lesions recognized may include those arising when translesion polymerases such as POLH incorporate bases across from DNA lesions caused by UV radiation. ..
  10. Mouret S, Charveron M, Favier A, Cadet J, Douki T. Differential repair of UVB-induced cyclobutane pyrimidine dimers in cultured human skin cells and whole human skin. DNA Repair (Amst). 2008;7:704-12 pubmed publisher
    Cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) are the two main classes of mutagenic DNA damages induced by UVB radiation...
  11. Spivak G, Cox R, Hanawalt P. New applications of the Comet assay: Comet-FISH and transcription-coupled DNA repair. Mutat Res. 2009;681:44-50 pubmed publisher
    ..We review the existing evidence and discuss the implications in relation to current models for the molecular mechanism of TCR. ..
  12. Alekseev S, Kool H, Rebel H, Fousteri M, Moser J, Backendorf C, et al. Enhanced DDB2 expression protects mice from carcinogenic effects of chronic UV-B irradiation. Cancer Res. 2005;65:10298-306 pubmed
    UV-damaged DNA-binding protein (UV-DDB) is essential for global genome repair (GGR) of UV-induced cyclobutane pyrimidine dimers (CPD)...
  13. Biverstål A, Johansson F, Jenssen D, Erixon K. Cyclobutane pyrimidine dimers do not fully explain the mutagenicity induced by UVA in Chinese hamster cells. Mutat Res. 2008;648:32-9 pubmed publisher
    UVA generates low levels of cyclobutane pyrimidine dimers (CPDs). Here we asked the question whether CPDs could fully explain the level of mutations induced by UVA...
  14. Law Y, Azadi J, Crespo Hernandez C, Olmon E, Kohler B. Predicting thymine dimerization yields from molecular dynamics simulations. Biophys J. 2008;94:3590-600 pubmed publisher
    ..hypothesis that conventional molecular dynamics simulations can be used to predict the yield of cyclobutane pyrimidine dimers in DNA...
  15. Li J, Uchida T, Ohta T, Todo T, Kitagawa T. Characteristic structure and environment in FAD cofactor of (6-4) photolyase along function revealed by resonance Raman spectroscopy. J Phys Chem B. 2006;110:16724-32 pubmed
  16. Navaraj A, Mori T, El Deiry W. Cooperation between BRCA1 and p53 in repair of cyclobutane pyrimidine dimers. Cancer Biol Ther. 2005;4:1409-14 pubmed
  17. Ueda T, Sato T, Hidema J, Hirouchi T, Yamamoto K, Kumagai T, et al. qUVR-10, a major quantitative trait locus for ultraviolet-B resistance in rice, encodes cyclobutane pyrimidine dimer photolyase. Genetics. 2005;171:1941-50 pubmed
    ..Furthermore, we were able to develop a UV-hyperresistant plant by overexpression of the photolyase gene. ..
  18. Wang H, Hoffman P, Lawrence C, Hays J. Testing excision models for responses of mismatch-repair systems to UV photoproducts in DNA. Environ Mol Mutagen. 2006;47:296-306 pubmed
    ..Even a substrate containing three T[CPD]T/AG photoproducts (in different contexts) did not significantly provoke excision. Thus, MMR may suppress UV mutagenesis by non-excisive mechanisms. ..
  19. Teng Y, Bennett M, Evans K, Zhuang Jackson H, Higgs A, Reed S, et al. A novel method for the genome-wide high resolution analysis of DNA damage. Nucleic Acids Res. 2011;39:e10 pubmed publisher
  20. Song Q, Sherrer S, Suo Z, Taylor J. Preparation of site-specific T=mCG cis-syn cyclobutane dimer-containing template and its error-free bypass by yeast and human polymerase ?. J Biol Chem. 2012;287:8021-8 pubmed publisher
    ..We also demonstrate that both yeast and human pol ? synthesize past the 3'-(m)C CPD in a >99% error-free manner, consistent with the highly water-exposed nature of the active site. ..
  21. El Mahdy M, Zhu Q, Wang Q, Wani G, Praetorius Ibba M, Wani A. Cullin 4A-mediated proteolysis of DDB2 protein at DNA damage sites regulates in vivo lesion recognition by XPC. J Biol Chem. 2006;281:13404-11 pubmed
    ..DDB2 degradation at the damage sites and regulates the recruitment of XPC and the repair of cyclobutane pyrimidine dimers. We have shown that CUL-4A can be identified in a UV-responsive protein complex containing both DDB subunits...
  22. Ziv O, Geacintov N, Nakajima S, Yasui A, Livneh Z. DNA polymerase zeta cooperates with polymerases kappa and iota in translesion DNA synthesis across pyrimidine photodimers in cells from XPV patients. Proc Natl Acad Sci U S A. 2009;106:11552-7 pubmed publisher
    Human cells tolerate UV-induced cyclobutane pyrimidine dimers (CPD) by translesion DNA synthesis (TLS), carried out by DNA polymerase eta, the POLH gene product...
  23. Su D, Fang H, Gross M, Taylor J. Photocrosslinking of human telomeric G-quadruplex loops by anti cyclobutane thymine dimer formation. Proc Natl Acad Sci U S A. 2009;106:12861-6 pubmed publisher
    ..Furthermore, these unusual anti photoproducts may be used to establish the presence of G-quadruplex or quadruplex-like structures in vivo. ..
  24. Zhou B, Luo D, Wei F, Chen X, Gao J. Baicalin protects human fibroblasts against ultraviolet B-induced cyclobutane pyrimidine dimers formation. Arch Dermatol Res. 2008;300:331-4 pubmed publisher the sites of incorrectly repaired DNA photoproducts, of which the most common are the cyclobutane pyrimidine dimers (CPDs). In this study, a DNA damage model of UVB irradiation-induced fibroblasts was established...
  25. Yeeles J, Marians K. The Escherichia coli replisome is inherently DNA damage tolerant. Science. 2011;334:235-8 pubmed publisher
    ..These observations reveal that the replisome can tolerate leading-strand template lesions without dissociating by synthesizing the leading strand discontinuously. ..
  26. Ikehata H, Ono T. The mechanisms of UV mutagenesis. J Radiat Res. 2011;52:115-25 pubmed
    ..Two models have been proposed: "error-free" bypass of deaminated cytosine-containing cyclobutane pyrimidine dimers (CPDs) by DNA polymerase ?, and error-prone bypass of CPDs and other UV-induced photolesions by combinations ..
  27. Yamamoto J, Tanaka Y, Iwai S. Spectroscopic analysis of the pyrimidine(6-4)pyrimidone photoproduct: insights into the (6-4) photolyase reaction. Org Biomol Chem. 2009;7:161-6 pubmed publisher
    ..The results of this study have implications not only for the recognition and reaction mechanisms of (6-4) photolyase, but also for the chemical nature of the (6-4) photoproduct. ..
  28. Köberle B, Roginskaya V, Wood R. XPA protein as a limiting factor for nucleotide excision repair and UV sensitivity in human cells. DNA Repair (Amst). 2006;5:641-8 pubmed
    ..No removal of cyclobutane pyrimidine dimers was detected in the SV40 immortalized cell lines tested...
  29. Vasquez Del Carpio R, Silverstein T, Lone S, Johnson R, Prakash L, Prakash S, et al. Role of human DNA polymerase ? in extension opposite from a cis-syn thymine dimer. J Mol Biol. 2011;408:252-61 pubmed publisher
    ..the 3'T of a cis-syn T-T dimer but is remarkably well adapted to accommodate the 5'T via Watson-Crick base pairing, in accord with a proposed role for Pol? in the extension reaction opposite from cyclobutane pyrimidine dimers in vivo.
  30. Wölfle U, Esser P, Simon Haarhaus B, Martin S, Lademann J, Schempp C. UVB-induced DNA damage, generation of reactive oxygen species, and inflammation are effectively attenuated by the flavonoid luteolin in vitro and in vivo. Free Radic Biol Med. 2011;50:1081-93 pubmed publisher
    ..In human skin, luteolin effectively reduced the formation of UVB-induced cyclobutane pyrimidine dimers. The free radical scavenging activity of luteolin was assessed in various cell-free and cell-based assays...
  31. Shachar S, Ziv O, Avkin S, Adar S, Wittschieben J, Reissner T, et al. Two-polymerase mechanisms dictate error-free and error-prone translesion DNA synthesis in mammals. EMBO J. 2009;28:383-93 pubmed publisher
  32. Garinis G, Mitchell J, Moorhouse M, Hanada K, de Waard H, Vandeputte D, et al. Transcriptome analysis reveals cyclobutane pyrimidine dimers as a major source of UV-induced DNA breaks. EMBO J. 2005;24:3952-62 pubmed
    ..effects of ultraviolet (UV) light on skin by providing a means to selectively remove either cyclobutane pyrimidine dimers (CPDs) or pyrimidine (6-4) pyrimidone photoproducts...
  33. Mouret S, Baudouin C, Charveron M, Favier A, Cadet J, Douki T. Cyclobutane pyrimidine dimers are predominant DNA lesions in whole human skin exposed to UVA radiation. Proc Natl Acad Sci U S A. 2006;103:13765-70 pubmed
    ..Cyclobutane pyrimidine dimers, a typical UVB-induced DNA damage, were found to be produced in significant yield also in whole human skin ..
  34. Teng Y, Liu H, Gill H, Yu Y, Waters R, Reed S. Saccharomyces cerevisiae Rad16 mediates ultraviolet-dependent histone H3 acetylation required for efficient global genome nucleotide-excision repair. EMBO Rep. 2008;9:97-102 pubmed
  35. Scrima A, Konícková R, Czyzewski B, Kawasaki Y, Jeffrey P, Groisman R, et al. Structural basis of UV DNA-damage recognition by the DDB1-DDB2 complex. Cell. 2008;135:1213-23 pubmed publisher
    ..The structure provides insights into damage recognition in chromatin and suggests a mechanism by which the DDB1-associated CUL4 ubiquitin ligase targets proteins surrounding the site of damage...
  36. Wakasugi M, Kasashima H, Fukase Y, Imura M, Imai R, Yamada S, et al. Physical and functional interaction between DDB and XPA in nucleotide excision repair. Nucleic Acids Res. 2009;37:516-25 pubmed publisher
    ..These results suggest that the physical interaction between DDB and XPA plays an important role in the DDB-mediated NER reaction. ..
  37. Auclair Y, Rouget R, Affar E, Drobetsky E. ATR kinase is required for global genomic nucleotide excision repair exclusively during S phase in human cells. Proc Natl Acad Sci U S A. 2008;105:17896-901 pubmed publisher
    ..g., UV-induced 6-4 photoproducts (6-4PPs) and cyclobutane pyrimidine dimers (CPDs)...
  38. Fishelevich R, Zhao Y, Tuchinda P, Liu H, Nakazono A, Tammaro A, et al. Imiquimod-induced TLR7 signaling enhances repair of DNA damage induced by ultraviolet light in bone marrow-derived cells. J Immunol. 2011;187:1664-73 pubmed publisher of UV light (UVL)-irradiated gene expression constructs and accelerated the resolution of cyclobutane pyrimidine dimers after UVL exposures in P388 and XS52...
  39. Besaratinia A, Yoon J, Schroeder C, Bradforth S, Cockburn M, Pfeifer G. Wavelength dependence of ultraviolet radiation-induced DNA damage as determined by laser irradiation suggests that cyclobutane pyrimidine dimers are the principal DNA lesions produced by terrestrial sunlight. FASEB J. 2011;25:3079-91 pubmed publisher
    ..e., cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts [(6-4)PPs], based on direct UV absorption of DNA, in irradiated mouse genomic ..
  40. Vu B, Cannistraro V, Sun L, Taylor J. DNA synthesis past a 5-methylC-containing cis-syn-cyclobutane pyrimidine dimer by yeast pol eta is highly nonmutagenic. Biochemistry. 2006;45:9327-35 pubmed
    Cyclobutane pyrimidine dimers (CPDs) are responsible for a considerable fraction of sunlight-induced C to T and 5-methycytosine (mC) to T mutations in mammalian cells, though the precise mechanism is unknown...
  41. Rünger T, Farahvash B, Hatvani Z, Rees A. Comparison of DNA damage responses following equimutagenic doses of UVA and UVB: a less effective cell cycle arrest with UVA may render UVA-induced pyrimidine dimers more mutagenic than UVB-induced ones. Photochem Photobiol Sci. 2012;11:207-15 pubmed publisher
    ..published data on the spectra of UVA-induced mutations in primary human skin cells and in mice suggest that pyrimidine dimers are the most common type of DNA damage-inducing mutations not only with UVB, but also with UVA...
  42. Tewari A, Sarkany R, Young A. UVA1 induces cyclobutane pyrimidine dimers but not 6-4 photoproducts in human skin in vivo. J Invest Dermatol. 2012;132:394-400 pubmed publisher
    UVB readily induces cyclobutane pyrimidine dimers, mainly thymine dimers (TTs), and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) in DNA. These lesions result in "UVB signature mutations" found in skin cancers...
  43. Mallet J, Rochette P. Ultraviolet light-induced cyclobutane pyrimidine dimers in rabbit eyes. Photochem Photobiol. 2011;87:1363-8 pubmed publisher
    ..It is well established that exposure to ultraviolet (UV) radiations leads to DNA damage, mainly cyclobutane pyrimidine dimers (CPDs). CPD formation is the principal factor involved in skin cancer...
  44. Yamada M, Udono M, Hori M, Hirose R, Sato S, Mori T, et al. Aged human skin removes UVB-induced pyrimidine dimers from the epidermis more slowly than younger adult skin in vivo. Arch Dermatol Res. 2006;297:294-302 pubmed
    Although many studies have been reported on the repair of ultraviolet light (UV)-induced cyclobutane-type pyrimidine dimers (CPDs) in DNA, the effects of aging on the removal of UV-induced CPDs from the human skin epidermis in vivo ..
  45. Szuts D, Marcus A, Himoto M, Iwai S, Sale J. REV1 restrains DNA polymerase zeta to ensure frame fidelity during translesion synthesis of UV photoproducts in vivo. Nucleic Acids Res. 2008;36:6767-80 pubmed publisher
  46. Yarosh D, Pena A, Nay S, Canning M, Brown D. Calcineurin inhibitors decrease DNA repair and apoptosis in human keratinocytes following ultraviolet B irradiation. J Invest Dermatol. 2005;125:1020-5 pubmed
    ..We found that both cyclosporine A (CsA) and ascomycin inhibited removal of cyclobutane pyrimidine dimers, and that they also inhibited UVB-induced apoptosis...
  47. Douki T. Effect of denaturation on the photochemistry of pyrimidine bases in isolated DNA. J Photochem Photobiol B. 2006;82:45-52 pubmed
    ..These results emphasize the modulating role of structure in the yield and nature of UV-induced DNA damage. ..
  48. Gaillard H, Wellinger R, Aguilera A. Methods to study transcription-coupled repair in chromatin. Methods Mol Biol. 2009;523:141-59 pubmed publisher
    ..About 90% of the photoproducts consist of cyclobutane pyrimidine dimers, which can be cleaved by the DNA nicking activity of the T4 endonuclease V (T4endoV) repair enzyme...
  49. Garcin G, Douki T, Stoebner P, Guesnet J, Guezennec A, Martinez J, et al. Cell surface expression of melanocortin-1 receptor on HaCaT keratinocytes and alpha-melanocortin stimulation do not affect the formation and repair of UVB-induced DNA photoproducts. Photochem Photobiol Sci. 2007;6:585-93 pubmed
    ..Similar levels of 8 bipyrimidine photoproducts including cyclobutane pyrimidine dimers (CPDs) (T<>T, T<>C, C<>T), (6-4) photoproducts ((6-4)PPs) (TT-(6-4)PPs, TC-(6-4)PPs) and ..
  50. El Mahdy M, Zhu Q, Wang Q, Wani G, Patnaik S, Zhao Q, et al. Naringenin protects HaCaT human keratinocytes against UVB-induced apoptosis and enhances the removal of cyclobutane pyrimidine dimers from the genome. Photochem Photobiol. 2008;84:307-16 pubmed
    ..of naringenin (NG), a naturally occurring citrus flavonone, on the removal of UVB-induced cyclobutane pyrimidine dimers (CPD) from the genome and apoptosis in immortalized p53-mutant human keratinocyte HaCaT cells...
  51. Kao Y, Saxena C, Wang L, Sancar A, Zhong D. Direct observation of thymine dimer repair in DNA by photolyase. Proc Natl Acad Sci U S A. 2005;102:16128-32 pubmed
    ..These results show that the photocycle of DNA repair by photolyase is through a radical mechanism and completed on subnanosecond time scale at the dynamic active site, with no net change in the redox state of the flavin cofactor. ..
  52. Biertümpfel C, Zhao Y, Kondo Y, Ramón Maiques S, GREGORY M, Lee J, et al. Structure and mechanism of human DNA polymerase eta. Nature. 2010;465:1044-8 pubmed publisher DNA polymerase eta (Poleta), a DNA polymerase that enables replication through ultraviolet-induced pyrimidine dimers. Here we report high-resolution crystal structures of human Poleta at four consecutive steps during DNA ..
  53. Walmacq C, Cheung A, Kireeva M, Lubkowska L, Ye C, Gotte D, et al. Mechanism of translesion transcription by RNA polymerase II and its role in cellular resistance to DNA damage. Mol Cell. 2012;46:18-29 pubmed publisher
    UV-induced cyclobutane pyrimidine dimers (CPDs) in the template DNA strand stall transcription elongation by RNA polymerase II (Pol II)...