PMID:15474419

Citation	Jurado, J, Maciejewska, A, Krwawicz, J, Laval, J and Saparbaev, MK (2004) Role of mismatch-specific uracil-DNA glycosylase in repair of 3,N4-ethenocytosine in vivo. DNA Repair (Amst.) 3:1579-90
Abstract	The 3,N(4)-ethenocytosine (epsilon C) residue might have biological role in vivo since it is recognized and efficiently excised in vitro by the E. coli mismatch-specific uracil-DNA glycosylase (MUG) and the human thymine-DNA glycosylase (hTDG). In the present work we have generated mug defective mutant of E. coli by insertion of a kanamycin cassette to assess the role of MUG in vivo. We show that human TDG complements the enzymatic activity of MUG when expressed in a mug mutant. The epsilon C-DNA glycosylase defective strain did not exhibit spontaneous mutator phenotype and did not show unusual sensitivity to any of the following DNA damaging treatments: methylmethanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, ultraviolet light, H(2)O(2), paraquat. However, plasmid DNA damaged by 2-chloroacetaldehyde treatment in vitro was inactivated at a greater rate in a mug mutant than in wild-type host, suggesting that MUG is required for the in vivo processing of the ethenobases. In addition, 2-chloroacetaldehyde treatment induces preferentially G.C --> C.G and A.T --> T.A transversions in mug mutant. Comparison of the mutation frequencies induced by the site-specifically incorporated epsilon C residue in E. coli wild-type versus mug indicates that MUG repairs more than 80% of epsilon C residues in vivo. Furthermore, the results show that nucleotide excision repair and recombination are not involved in the processing of epsilon C in E. coli. Based on the mutagenesis data we suggest that epsilon C may be less toxic and less mutagenic than expected. The increased spontaneous mutation rate for G.C --> A.T transition in the ung mug double mutant as compared to the single ung mutant suggest that MUG may be a back-up repair enzyme to the classic uracil-DNA glycosylase.
Links	PubMed Online version:10.1016/j.dnarep.2004.06.012
Keywords	Acetaldehyde/analogs & derivatives; Acetaldehyde/pharmacology; Base Pair Mismatch/genetics; Base Pair Mismatch/physiology; Cytosine/analogs & derivatives; Cytosine/metabolism; DNA Damage/genetics; DNA Repair/genetics; DNA Repair/physiology; Escherichia coli/enzymology; Escherichia coli/genetics; Genetic Complementation Test; Humans; Microbial Sensitivity Tests; Mutagenesis, Insertional/genetics; Mutagens/pharmacology; Mutation/genetics; Plasmids/drug effects; Plasmids/metabolism; Thymine DNA Glycosylase/genetics; Thymine DNA Glycosylase/physiology
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