| Abstract
| - Single-stranded DNA genomes have been constructed that site-specifically contain the 7,8-dihydro-8-oxo-2‘-deoxyguanine (8-oxoG) oxidation products guanidinohydantoin (Gh) and the two stablestereoisomers of spiroiminodihydantoin (Sp1 and Sp2). The circular viral genomes were transfected intowild-type AB1157 Escherichia coli, and the efficiency of lesion bypass by DNA polymerase(s) wasassessed. Viral progeny were analyzed for mutation frequency and type using the recently developedrestriction endonuclease and postlabeling (REAP) assay. Gh was bypassed nearly as efficiently as theparent 8-oxoG but was highly mutagenic, causing almost exclusive G → C transversions. The stereoisomersSp1 and Sp2 were, in comparison, much stronger blocks to DNA polymerase extension and caused amixture of G → T and G → C transversions. The ratio of G → T to G → C mutations for each Sp lesionwas dependent on the stereochemical configuration of the base. All observed mutation frequencies wereat least an order of magnitude higher than those caused by 8-oxoG. Were these lesions to be formed invivo, our data show that they are absolutely miscoding and may be refractory to repair after translesionsynthesis.
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