Hypersensitivity of XP-V cells to psoralen photoadducts. A) Whole cell lysates of XP30RO/c15 (XP-V/pol η) and XP30RO/cDNA3 (XP-V/cDNA) cells were analyzed by Western immunoblotting for pol η expression, using actin as a loading control. B) Cytotoxicity following HMT and UVA treatment. XP-V/pol η(•, ■) and XP-V/cDNA (○, □) were exposed to increasing concentrations of either HMT, and then irradiated with either a single dose of 5 kJ/m2 UVA (•,○), or a split-dose UVA protocol consisting of 5 kJ/m2, followed by rinsing with HBSS to remove unbound HMT and then re-irradiation with 15 kJ/m2 (■,□)). Cells were then replaced in media and incubated for 3 days before survival was assessed. Error bars denote standard deviation.