Comparative survival of aminobiphenyl- and aminofluorene- substituted plasmid DNA in Escherichia coli Uvr endonuclease deficient strains

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Abstract
PBR322 plasmid DNA, randomly substituted with arylamine moieties, was introduced into Escherichia coli Uvr endonuclease deficient strains. Plasmid survival was determined by selection in the presence of ampicillin. Modification of plasmid DNA with N-acetoxy-N-trifluoroitcetylamiwbiphenyl yielded primarily N-(deoxyguanosin-8-yl)-4-aminobiphenyl residues. Reaction of DNA with N-acetoxy-N-acetylamino-biphenyl produced only N-(deoxyguanclsin-8-yl)-4-acetylarninobiphenyl adducts. The arninobiphenyl (ABP) and acetylaminobiphenyl adducts reduced the ability of the plasmid DNA to transform E.coli to approximately the same extent in a wild-type strain. In uvrA, uvrB and uvrC, i.e. Uvr endonuclease deficient strains, both adducts produced equivalent decreases in survival, however, the reduction in survival was much more pronounced in the uvr-cells than in the wild-type strain. A similar pattern of toxicity was observed with plasmids carrying N-(deoxyguanosin-8-yl)-2-acetylaminofluorene adducts, although the acetylaminofluorene addud was - 5-fold more effective in reducing the biological activity of the plasmid. In contrast, the deacetylated aminofluorene (AF) lesion, N-(deoxyguanosin-8-y1)-2-aminofluorene, exhibited relatively Little effect on plasmid survival in uvrA and uvrB cells as compared to the wild-type strain, even though the survival of both ABP and AP adducts was essentially similar in the uvrC and wild-type strains. These data demonstrate that (i) both the deacetylated and acetylated lesions are subject to repair by the Uvr endonuclease complex, and (ii) the presence of the N-acetyl group is not the sole determinant of the differential effects of arylamine adducts in uvr cells. These observations provide indirect evidence that both the N-acetyl and aryl moieties of these adducts alter the conformation of DNA.

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