Figure 1.

Schematic representation of the “mirror” method. A single-stranded DNA molecule containing 7,8-dihydro-8-oxoguanine (8-oxoG; X) is used as a template for synthesis of “mirror” products that exist as double-stranded hybrids with their original template. Depending on whether a particular “mirror” molecule was synthesized in an error-free or error-prone manner, it will contain either C or A opposite 8-oxoG, respectively. To eliminate any further influence of the 8-oxoG-containing template, asymmetric PCR is performed, yielding single-stranded DNA molecules containing either G or T in place of the original 8-oxoG. The former, when treated with EcoRI after conversion to double strand form, is left intact, whereas the latter is cleaved by EcoRI in its double strand form. Pol: DNA polymerase.