Fig. 6.

Photooxidation of SBrdU. (A and B) Photodestruction: An aqueous solution (100 μM) of SBrdU was irradiated with the indicated doses of UVA. Photoproducts were separated by HPLC and monitored at 260 and 342 nm. Products were quantified by comparison to authentic standards and data are expressed as Mole% of the unirradiated SBrdU. For the unidentified SBrdU irradiation product eluting at 18.7 min (panel B), values are expressed as A₃₄₂ peak area (μV × s). Traces corresponding to (A) are shown in Supplementary Fig. 4. (C and D) MMPP oxidation: An aqueous solution of SBrdU (100 μM) was treated with MMPP for 20 min at the indicated molar ratios and analysed by HPLC as above. (E) Photodestruction of DNA SBrdU: Cells that had been grown in 100 μM SBrdU for 24 h and in which SBrdU replaced approximately 0.06% of DNA TdR were UVA irradiated at the indicated doses. DNA was extracted, digested to nucleosides and analysed by HPLC as in A. As SBrdU was the only nucleoside detected at 342 nm, recovered SBrdU is expressed as percentage SBrdU in DNA from unirradiated cells.