HeLa cells were transfected with pCMV-Tax and 48 hours later processed for immunofluorescence analysis using antibodies against Tax (red, panel C), Ku80 (green, panels B and C) and counter-stained with DAPI (blue, panel A) to visualize nuclei. Arrows point to cells that stain positively for Tax. This experiment was repeated three times and cell counts from one representative experiment are shown in panel D. Cells that showed reduced Ku80 staining, such as those indicated by arrows in panel B were scored as Ku80 negative. Cells that showed intense diffuse nuclear staining were scored as Ku80 positive. Tax immunostaining was used to score cells as Tax positive and Tax negative.