Mutagenic target for hydroxyl radicals generated in Escherichia coli mutant deficient in Mn- and Fe- superoxide dismutases and Fur, a repressor for iron-uptake systems.
We previously reported that mutations in Mn- and Fe-superoxide dismutases and Fur, a repressor for iron uptake systems, simulated generation of hydroxyl radicals, and caused hypermutability in Escherichia coli. The predominant type of spontaneous mutation was GC --> TA, followed by AT --> CG, suggesting the involvement of 7,8-dihydro-8-oxoguanine (8-oxoG) and 1,2-dihydro-2-oxoadenine (2-oxoA) in DNA as well as 7,8-dihydro-8-oxodeoxyguanosine triphosphate (8-oxodGTP) and 1,2-dihydro-2-oxodeoxyadenosine triphosphate (2-oxodATP) in the nucleotide pool. To determine the targets contributing to oxidative mutagenesis, DNA or nucleotides, we characterized spontaneous mutations and compared the distribution to those in mutMY and mutT strains, in which GC --> TA and AT --> CG were predominantly induced, respectively. The hotspots and sequence contexts where AT --> CG occurred frequently in sodAB fur strain were almost identical to those in mutT strain,whereas, those where GC --> TA occurred frequently in sodAB fur strain were quite different from those in mutMY strain. These observations suggested that AT --> CG is due to 8-oxodGTP, while GC --> TA is produced by some other lesion(s). The 2-oxodATP is also a major oxidative lesion in nucleotides, and strongly induces GC --> TA. The expression of cDNA for MTH1, which can hydrolyze 2-oxodATP as well as 8-oxodGTP, partially but significantly, suppressed the GC --> TA mutator phenotype of the sodAB fur strain, whereas, it did not for the mutMY strain. Additionally, the sequence contextby 2-oxodATP in E. coli was similar to that in sodAB fur strain. These results suggested that the targets contributing to oxidative mutagenesis in sodAB fur strain are nucleotides such as dGTP and dATP, rather than DNA.
Nunoshiba
Tatsuo
T
Department of Biomolecular Science, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8577, Japan. tnuno@mail.cc.tohoku.ac.jp
Watanabe
Takashi
T
Nakabeppu
Yusaku
Y
Yamamoto
Kazuo
K
D020856:AT Rich Sequence / Q000235:genetics; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D045647:DNA Glycosylases; D004260:DNA Repair; D043382:DNA-Formamidopyrimidine Glycosylase; D003838:Deoxyadenine Nucleotides / Q000235:genetics; D003848:Deoxyguanine Nucleotides / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D020862:GC Rich Sequence / Q000235:genetics; D016153:Genes, Suppressor; D017665:Hydroxyl Radical / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009699:N-Glycosyl Hydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D011755:Pyrophosphatases; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000172:deficiency* / Q000378:metabolism
D001426:Bacterial Proteins; D003838:Deoxyadenine Nucleotides; D003848:Deoxyguanine Nucleotides; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; C096275:supF tRNA; C078206:8-oxodeoxyguanosine triphosphate; D017665:Hydroxyl Radical; D008345:Manganese; D012343:RNA, Transfer; D007501:Iron; D013482:Superoxide Dismutase; D010744:Phosphoric Monoester Hydrolases; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C061738:mutY adenine glycosylase; D043382:DNA-Formamidopyrimidine Glycosylase; C468610:DNA-formamidopyrimidine glycosylase, E coli; D011755:Pyrophosphatases; C052211:mutT protein, E coli