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The processing of a unique 8-oxoguanine residue in DNA has been studied in mammalian cells using a single-stranded shuttle vector. A fragment of human Ha-ras carrying the lesion on the first (G1) or the second guanine (G2) of codon 12 was inserted in a shuttle plasmid. Extrachromosomal DNA is replicated in animal cells, extracted and used to transform bacteria to be amplified and individualized. DNA sequencing of bacterial clones showed the mutagenic potency of 8-oxoguanine in vivo to be approximately 4%. The presence of the 8-oxoguanine does not greatly affect survival of the progeny. No significant difference was observed between the mutation frequencies induced by 8-oxoguanine located either at the G1 or G2 position. The majority of the mutations, targeted at the lesion level, are G to T transversions. These base substitutions induced respectively glycine to cysteine (G1) or valine (G2) change in the P21ras protein. These mutations may contribute to activation of the protooncogene, leading to spontaneous tumorigenesis.
Page et al. (Sun,) studied this question.