Abstract
Ionizing radiation induces various DNA damage localized closely along its track. The resulted damaged site including two or more lesions within two helical turns of DNA is called clustered damage. Especially, bistranded clustered damage is thought to be unrepairable, and lead to cell death and mutations. Double-strand break, as bistranded strand break cluster, is processed by non-homologous end-joining. On the other hand, bistranded clustered base damage is supposed to be processed by base excision repair. However, enzymatic efficiency of each DNA-glycosylase for clustered base damage has been unclear. We examined the enzymatic activity of DNA-glycosylases for oxidative base lesions in clustered damage in this study. Oligonucleotide substrates containing two bistranded base lesions were prepared, such as thymine glycol, urea, and 8-oxoguanine. The distance between two lesions was set 1, 3 or 5 nucleotide away for upstream or downstream on each substrate. Activities of Escherichia coli endonuclease III, VIII, and Fpg, and these human homologues for the clustered substrates were assessed by nicking assay. As a result, activities of tested DNA-glycosylases were affected by the distance and the species of lesions.
