title: UVA generates pyrimidine dimers in DNA directly.
abstract: There is increasing evidence that UVA radiation, which makes up approximately 95% of the solar UV light reaching the Earth's surface and is also commonly used for cosmetic purposes, is genotoxic. However, in contrast to UVC and UVB, the mechanisms by which UVA produces various DNA lesions are still unclear. In addition, the relative amounts of various types of UVA lesions and their mutagenic significance are also a subject of debate. Here, we exploit atomic force microscopy (AFM) imaging of individual DNA molecules, alone and in complexes with a suite of DNA repair enzymes and antibodies, to directly quantify UVA damage and reexamine its basic mechanisms at a single-molecule level. By combining the activity of endonuclease IV and T4 endonuclease V on highly purified and UVA-irradiated pUC18 plasmids, we show by direct AFM imaging that UVA produces a significant amount of abasic sites and cyclobutane pyrimidine dimers (CPDs). However, we find that only approximately 60% of the T4 endonuclease V-sensitive sites, which are commonly counted as CPDs, are true CPDs; the other 40% are abasic sites. Most importantly, our results obtained by AFM imaging of highly purified native and synthetic DNA using T4 endonuclease V, photolyase, and anti-CPD antibodies strongly suggest that CPDs are produced by UVA directly. Thus, our observations contradict the predominant view that as-yet-unidentified photosensitizers are required to transfer the energy of UVA to DNA to produce CPDs. Our results may help to resolve the long-standing controversy about the origin of UVA-produced CPDs in DNA.
authors.affiliation: Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, North Carolina, USA.
authors.forename: Yong
authors.initials: Y
authors.lastname: Jiang
authors.forename: Mahir
authors.initials: M
authors.lastname: Rabbi
authors.forename: Minkyu
authors.initials: M
authors.lastname: Kim
authors.forename: Changhong
authors.initials: C
authors.lastname: Ke
authors.forename: Whasil
authors.initials: W
authors.lastname: Lee
authors.forename: Robert L
authors.initials: RL
authors.lastname: Clark
authors.forename: Piotr A
authors.initials: PA
authors.lastname: Mieczkowski
authors.forename: Piotr E
authors.initials: PE
authors.lastname: Marszalek
mesh_terms: D000906:Antibodies / Q000276:immunology; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D004249:DNA Damage; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism; D043224:Deoxyribonuclease (Pyrimidine Dimer) / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D018625:Microscopy, Atomic Force; D010957:Plasmids / Q000378:metabolism; D011740:Pyrimidine Dimers / Q000276:immunology / Q000378:metabolism*; D012680:Sensitivity and Specificity; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000378:metabolism; D014867:Water / Q000494:pharmacology
chemical_list: D000906:Antibodies; D011740:Pyrimidine Dimers; D014764:Viral Proteins; D014867:Water; D004247:DNA; C470698:endonuclease V, phage T4; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004255:Deoxyribodipyrimidine Photo-Lyase