title: Protection against UV-induced pyrimidine dimerization in DNA by triplex formation.
abstract: Cyclobutane and [6-4]-pyrimidine dimers are major photoproducts of ultraviolet-irradiated DNA. The yield of these photoproducts is dependent on the sequence and structure of the DNA. By analysing the photofootprints of fragments produced by cleavage of the DNA chain near [6-4]-pyrimidine dimers, we show here that a homopurine-homopyrimidine insert (with either d(TC)x or d(C)n) in plasmid pUC19 is, as expected, a good target for UV-induced pyrimidine-dimer formation. But we find that dimerization is virtually completely suppressed when the pyrimidine oligonucleotides d(TC)y or d(C)m are added to DNA carrying d(TC)x- or d(C)n-containing inserts, respectively. This effect is dependent on the type of oligonucleotide used and is site-specific. The protection occurs under acidic conditions that favour the formation of intermolecular triplexes between the homopurine-homopyrimidine inserts and homologous oligopyrimidines. We therefore conclude that triplex formation effectively protects the DNA duplex from UV-induced damage (pyrimidine dimerization). This observation makes the photofootprinting assay a very promising method for studying intermolecular and intramolecular triplexes (H-form DNA) both in vitro and in vivo.
authors.affiliation: Department of Molecular Genetics, Ohio State University, Columbus 43210-1292.
authors.forename: V I
authors.initials: VI
authors.lastname: Lyamichev
authors.forename: M D
authors.initials: MD
authors.lastname: Frank-Kamenetskii
authors.forename: V N
authors.initials: VN
authors.lastname: Soyfer
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000378:metabolism* / Q000528:radiation effects; D004262:DNA Restriction Enzymes; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D010957:Plasmids; D011089:Polydeoxyribonucleotides / Q000378:metabolism; D011740:Pyrimidine Dimers / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D009838:Oligodeoxyribonucleotides; D011089:Polydeoxyribonucleotides; D011740:Pyrimidine Dimers; D004247:DNA; D004262:DNA Restriction Enzymes