FIG. 1.

Dose-dependent inhibition of cellular DNA repair by Tax. (A) UDS assay. REF52 fibroblasts were transfected with increasing concentrations of Tax expression plasmid pSV-Tax (0.5 to 2 μg) or 2 μg of negative control plasmid pSV-TaxΔHC (a Tax frameshift mutant plasmid) or pSV2-neo. The cells were serum starved, one dish of each duplicate was UV irradiated, and all cells were labeled with [³H]thymidine for 3 h. After labeling, the cells were lysed and the precipitated DNA was counted. The percent repair activity was calculated as described in Materials and Methods. The error bars indicate the standard deviations of three replicates. (B) HCR assay. The pMSV-Luc plasmid was UV irradiated and cotransfected into REF52 fibroblasts with increasing concentrations of Tax expression plasmid pCMV-Tax (0.25 to 1 μg) or 1 μg of negative control backbone plasmid pCMV-1. Duplicate dishes received the same transfection mixture except that the pMSV-Luc plasmid was not irradiated in one dish. Forty hours following transfection, the cells were harvested and luciferase and CAT assays were performed. Percent repair activity was calculated as described in Materials and Methods. The error bars indicate the standard deviations of three replicates.