FIGURE 1.

Experimental outline. A, chemical structures of guanine (G), ^SG, and S⁶mG. B, strategy for assessing the impact of ^SG and S⁶mG on DNA transcription. X indicates an ^SG, S⁶mG, or guanine that was located on the transcribed strand of TurboGFP gene downstream of the CMV and T7 promoters. The +1 transcription start sites are indicated as arrows. Lesion-bearing or control plasmids were mixed with the competitor genome as DNA templates for in vitro or in vivo transcription. Although truncated RNA may be produced when transcription arrests at or near a lesion site, only run-off RNA is shown and used for RT-PCR. Among the RT-PCR products, only the wild-type sequence arising from the lesion-containing genome is shown. The arrows indicate the cleavage sites of SacI and FspI, which are used to digest the RT-PCR products for subsequent PAGE and LC-MS/MS analyses.