Abstract
Ionizing radiation induces various types of DNA lesions, such as strand breaks, oxidative base lesions and, in particular, biologically relevant complex damage known as clustered DNA damage sites, which consist of two or more elemental lesions within two helical turns of DNA. Recent in vitro studies have shown that the repair of lesions within clusters may be retarded, but less in known about the mutagenic effects of clustered damage in vivo. We have investigated the mutagenic potential of bistranded clustered damage site which consists of 8-oxo-7, 8-dihydroguanine (8-oxoG) and thymine glycol (TG), with 8-oxoG placed within a restriction site on one strand and TG positioned at site 1 bp away on the opposing strand. Damaged DNA was transfected into wild-type and glycosylase deficient mutant cells (fpg, mutY, nth, nei, fpg mutY, nth fpg mutY, fpg mutY nei) of E. coli, and mutations were determined by inability to cut the restriction site. Mutation frequencies were found to be significantly higher for the clustered TG + 8-oxoG lesions than for each of the single lesions, suggesting that the repair of the clustered damage site is retarded. The results of the mutation frequencies for clustered TG + 8-oxoG lesion and our previous results for dihydrothymine (DHT)+ 8-oxoG will be compared and discussed.
