title: Cyclobutane pyrimidine dimers are responsible for the vast majority of mutations induced by UVB irradiation in mammalian cells.
abstract: The most prevalent DNA lesions induced by UVB are the cyclobutane pyrimidine dimers (CPDs) and the pyrimidine (6-4) pyrimidone photoproducts ((6-4)PPs). It has been a long standing controversy as to which of these photoproduct is responsible for mutations in mammalian cells. Here we have introduced photoproduct-specific DNA photolyases into a mouse cell line carrying the transgenic mutation reporter genes lacI and cII. Exposure of the photolyase-expressing cell lines to photoreactivating light resulted in almost complete repair of either CPDs or (6-4)PPs within less than 3 h. The mutations produced by the remaining, nonrepaired photoproducts were scored. The mutant frequency in the cII gene after photoreactivation by CPD photolyase was reduced from 127 x 10(-5) to 34 x 10(-5) (background, 8-10 x 10(-5)). Photoreactivation with (6-4) photolyase did not lower the mutant frequency appreciably. In the lacI gene the mutant frequency after photoreactivation repair of CPDs was reduced from 148 x 10(-5) to 28 x 10(-5) (background, 6-10 x 10(-5)). Mutation spectra obtained with and without photoreactivation by CPD photolyase indicated that the remaining mutations were derived from background mutations, unrepaired CPDs, and other DNA photopoducts including perhaps a small contribution from (6-4)PPs. We conclude that CPDs are responsible for at least 80% of the UVB-induced mutations in this mammalian cell model.
authors.affiliation: Department of Biology, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA.
authors.forename: Y H
authors.initials: YH
authors.lastname: You
authors.forename: D H
authors.initials: DH
authors.lastname: Lee
authors.forename: J H
authors.initials: JH
authors.lastname: Yoon
authors.forename: S
authors.initials: S
authors.lastname: Nakajima
authors.forename: A
authors.initials: A
authors.lastname: Yasui
authors.forename: G P
authors.initials: GP
authors.lastname: Pfeifer
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000235:genetics; D019281:Dimerization; D004307:Dose-Response Relationship, Radiation; D015151:Immunoblotting; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D011743:Pyrimidines / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014466:Ultraviolet Rays
chemical_list: D011743:Pyrimidines; D004247:DNA; D004255:Deoxyribodipyrimidine Photo-Lyase; C030986:pyrimidine