Cockayne syndrome (CS) is a human genetic disorder characterized by sensitivity to UV radiation, neurodegeneration, premature aging among other phenotypes. CS complementary group B (CS-B) gene (csb) encodes the CSB protein (CSB) that is involved in base excision repair of a number of oxidatively induced lesions in genomic DNA in vivo. We hypothesized that CSB may also play a role in cellular repair of the helix-distorting tandem lesion (5'S)-8,5'-cyclo-2'-deoxyadenosine (S-cdA). Among many DNA lesions, S-cdA is unique in that it represents a concomitant damage to both the sugar and base moieties of the same nucleoside. Because of the presence of the C8 C5' covalent bond, S-cdA is repaired by nucleotide excision repair unlike most of other oxidatively induced lesions in DNA, which are subject to base excision repair. To test our hypothesis, we isolated genomic DNA samples from brain, kidney and liver of wild type and csb knockout (csb / ) mice. Animals were not exposed to any exogenous oxidative stress before the experiment. DNA samples were analyzed by liquid chromatography/mass spectrometry with isotope-dilution. Statistically greater background levels of S-cdA were observed in all three organs of csb / mice than in those of wild type mice. These results suggest in vivo accumulation of S-cdA in genomic DNA due to lack of its repair in csb / mice. Thus, this study provides, for the first time, the evidence that CSB plays a role in nucleotide excision repair of the DNA helix-distorting tandem lesion S-cdA. Accumulation of unrepaired S-cdA in vivo may contribute to the pathology associated with CS.
Citation: Dna Repair
Pub Type: Journals
Cockayne syndrome, 8, 5'-Cyclopurine-2'-deoxynucleosides, Hydroxyl radical, Mass spectrometry, Oxidative DNA damage