A. A. XPCKD and KIN17KD HeLa cells grow poorly 2 weeks after transfection. Forty-eight hours after transfection, cells were plated at the same density and grown in the presence of 250 μg/mL hygromycin B. Fourteen days later, clones were fixed and stained before counting. Columns, mean of three culture dishes; bars, SE. The experiments were replicated more than three times. For each cell line, results are expressed as a percentage of the control cell line. B. Higher UVC sensitivity of XPCKD HeLa cells compared with XPAKD and KIN17KD syngeneic HeLa cells. Clonogenic cell growth assays after UVC irradiation (4 J/m2) were carried out at different times following transfection with control cells (BD650), KIN17KD, XPCKD, or XPAKD HeLa. Cells were seeded at 500 cells per 6 cm diameter dish, irradiated 24 hours later, and analyzed after 14 days of culture. Columns, mean of three culture dishes; bars, SE. Results are expressed as a percentage of the control cell line (BD650) for each UVC irradiation experiment. C. Impaired unscheduled DNA synthesis in XPAKD and XPCKD clones after UVC irradiation. HeLa XPAKD (clones 3 and 6; day 110 after transfection) and XPCKD (clones 21 and 24; day 193) were plated onto coverslips in a growth suppression medium. Cells were irradiated and analyzed as described in Materials and Methods. The level of DNA repair is expressed as number of grains per nucleus as a function of UV dose. Denis S.F. Biard et al. Mol Cancer Res 2005;3:519-529 ©2005 by American Association for Cancer Research