RESUMEN
Nucleobase radicals are a major family of reactive species produced in DNA as a result of oxidative stress. Two such radicals, 5-hydroxy-5,6-dihydrothymidin-6-yl radical (1) and 5,6-dihydrouridin-6-yl radical (5), were independently generated within chemically synthesized oligonucleotides from photochemical precursors. Neither nucleobase radical produces direct strand breaks or alkali-labile lesions in single or double stranded DNA. The respective peroxyl radicals, resulting from O2 trapping, add to 5'-adjacent nucleobases, with a preference for dG. Distal dG's are also oxidatively damaged by the peroxyl radicals. Experiments using a variety of sequences indicate that distal damage occurs via covalent modification of the 5'-adjacent dG, but there is no evidence for electron transfer by the nucleobase peroxyl radicals.
Asunto(s)
ADN/química , Radicales Libres/química , Peróxidos/química , Pirimidinas/química , Secuencia de Bases , ADN/genética , Daño del ADN , Conformación de Ácido Nucleico , Oxidación-ReducciónRESUMEN
Photolysis of an aryl sulfide-containing 5,6-dihydropyrimidine (1) at 350 nm produces high yields of thymidine and products resulting from trapping of a 5,6-dihydrothymidin-5-yl radical by O2 or thiols. Thymidine is believed to result from disproportionation of the radical pair originally generated from C--S bond homolysis of 1 on the microsecond timescale, which is significantly shorter than other photochemical transformations of modified nucleotides into their native forms. Duplex DNA containing 1 is destabilized, presumably due to disruption of π-stacking. Incorporation of 1 within the binding site of the restriction endonuclease EcoRV provides a photochemical switch for turning on the enzyme's activity. In contrast, 1 is a substrate for endonuclease VIII and serves as a photochemical off switch for this base excision repair enzyme. Modification 1 also modulates the activity of the 10-23 DNAzyme, despite its incorporation into a nonduplex region. Overall, dihydropyrimidine 1 shows promise as a tool to provide spatiotemporal control over DNA structure on the miscrosecond timescale.
Asunto(s)
ADN/química , Timidina/química , ADN/metabolismo , ADN Catalítico/química , ADN Catalítico/metabolismo , Radicales Libres/química , Radicales Libres/metabolismo , Conformación de Ácido Nucleico , Procesos Fotoquímicos , Timidina/análogos & derivados , Timidina/metabolismoRESUMEN
C1027 is a potent antitumor agent that damages DNA. It has the unusual ability to produce double strand breaks and interstrand cross-links (ICLs) intracellularly, which enable it to initiate concurrent ataxia-telangiestasia mutated (ATM) and Rad-3 related (ATR) independent damage responses. The latter form of damage is not well characterized. We have examined the effect of DNA sequence on C1027 reactivity and found it to be more diverse than previously thought. In addition, analysis of the chemical stability of ICLs suggests that they result from reaction with the deoxyribose ring on one strand but direct addition to a nucleobase on the opposite strand.
Asunto(s)
Aminoglicósidos/farmacología , ADN/efectos de los fármacos , Enediinos/farmacología , Hidrógeno/química , Aminoglicósidos/química , Daño del ADN , Enediinos/química , Estructura Molecular , PlásmidosRESUMEN
5,6-Dihydro-5-hydroxythymidin-6-yl radical (1), the major reactive intermediate resulting from hydroxyl radical addition to C5 of the pyrimidine, is produced via 350 nm photolysis of a 2,5-dimethoxyphenylsulfide precursor (2). Competition between O(2) and thiol for 1 suggests that the radical reacts relatively slowly with ß-mercaptoethanol compared to other alkyl radicals. Overall, aryl sulfide 2 should be an effective precursor for the major hydroxyl radical adduct of thymidine in DNA.