8-hydroxyguanine and 2-nitrofluorene

8-Hydroxyguanine (8-OH-G) DNA glycosylase is an enzyme involved in repair of oxidative DNA damage, e.g., 8-OH-G in DNA. In order to assess the roles of 8-OH-G in spontaneous and chemically-induced mutagenesis, the mutMST gene encoding 8-OH-G DNA glycosylase of Salmonella typhimurium was disrupted in several Ames tester strains, i.e., S. typhimurium TA1535 (hisG46, uvrB-, rfa), TA1975 (hisG46, uvr+, rfa) and TA102 (hisG428, uvr+, rfa). The spontaneous mutation frequencies were increased 2.4 and 1.6 times, respectively, by the mutMST deletions in strains TA1535 and TA1975, which are spontaneously reverted to His+ by mutations mainly at G:C base pairs. The resulting strains YG3001 (TA1535 delta mutMST) and YG3002 (TA1975 delta mutMST) were 2 to 8 times more sensitive to the mutagenicities of methylene blue plus visible light, neutral red plus visible light and 2-nitrofluorene than the parent strains. The strain YG3002 but not YG3001 was about 30 times more sensitive to the mutagenicity of 4-nitroquinoline N-oxide than the parent strain TA1975. Neither hydrogen peroxide nor phenazine methosulfate was mutagenic in the mutMST-deletion strains as well as in the parent strains. In contrast, the mutMST deletion did not affect the spontaneous mutation frequency of strain TA102, which has an A:T base pair at the critical site for reversion. The sensitivities of strain TA102 to the chemicals were not enhanced by the mutMST deletion except for hydrogen peroxide. These results suggest that 8-OH-G in DNA plays important roles in spontaneous mutagenesis occurring at G:C base pairs in S. typhimurium, and some nitro aromatics such as 4-nitroquinoline N-oxide or 2-nitrofluorene as well as the photosensitizers plus visible light can produce 8-OH-G in DNA, thereby inducing mutations. In the case of 4-nitroquinoline N-oxide, 8-OH-G rather than DNA adducts seems to play major roles in mutagenesis in uvr+ background. The new strains could be useful for the evaluation of the roles of 8-OH-G in mutagenesis in S. typhimurium and permit the efficient detection of some oxidative mutagens in the environment.

Topics: 4-Nitroquinoline-1-oxide; Amino Acid Sequence; Base Sequence; Chromosome Mapping; Coloring Agents; DNA Repair; DNA-Formamidopyrimidine Glycosylase; Fluorenes; Genetic Markers; Guanine; Methylene Blue; Molecular Sequence Data; Mutagenesis, Insertional; Mutagenicity Tests; Mutagens; N-Glycosyl Hydrolases; Neutral Red; Salmonella typhimurium