Figure 6.

UVA photoproducts in oligonucleotides containing S⁴TdR with a 5′T. The oligonucleotide TS⁴TG annealed to a complementary strand to place a single S⁴T:A base pair 3′ to T:A base pair was irradiated with 10 kJ/m² UVA. Following digestion to nucleosides, the products were analysed by RP-HPLC and the eluate monitored by: (A) A₃₃₅. Upper trace unirradiated. Lower trace 10 kJ/m² UVA. The absorbance scale is the same for both traces. The arrow indicates S⁴TdR eluting at 26 min. (B) Fluorescence (Ex 320 nm; Em 370 nm). Upper trace unirradiated. Lower RP-HPLC trace 10 kJ/m² UVA. The arrow indicates the fluorescent photoproduct eluting at 19 min. Fluorescence scale is the same for both traces. (C) UVA dose dependence of S⁴TdR destruction. Residual S⁴TdR in digests of irradiated TS⁴TG duplexes was quantified from A₃₃₅ nm absorbance following HPLC separation. (D) UVA dose dependence of the formation of the fluorescent (D) and 315 nm absorbing (E) photoproduct eluting from HPLC at 19 min.