Tandem double CC-->TT mutations are produced by reactive oxygen species.

Oxidative damage to DNA is mutagenic and thus may play a role in carcinogenesis. Because of the large number of different DNA lesions formed by oxidative species, no genetic alteration so far identified is exclusively associated with oxygen damage. Tandem double CC-->TT mutations are known to occur via UV damage to DNA and are thought to be a specific indicator of UV exposure. Using a sensitive reversion assay that can detect both single and double mutations within the same codon of the M13-encoded lacZ alpha gene, we show that treatments that produce reactive oxygen species can also produce tandem double CC-->TT mutations. The frequency at which these mutations occur is less than that for single base mutations by a factor of approximately 30. The induction of these mutations is inhibited by treatment that scavenges hydroxyl radicals. This unique mutation provides a marker of oxygen free radical-induced mutagenesis in cells that are not exposed to UV-irradiation and an indicator for assessing the involvement of oxidative damage to DNA in aging and tumor progression.