Comparison of the enzymatic activities of the HSV-TK-Luc fusion protein, HSV-TK, and Luc. U87MG cells were transiently transfected with 0.05 – 2 μg of HSV-TK-Luc, Luc, or HSV-TK plasmid. Cells transfected with equimolar amounts of DNA were analyzed for cytotoxic and bioluminescent activity. (A) Cytotoxic activity of cells transfected with HSV-TK-Luc or HSV-TK. For reasons of clarity only the graphs for 0.1 μg and 2 μg of transfected DNA are shown. (B) Luciferase activity in U87MG cells transfected with HSV-TK-Luc or Luc only. Results represent 3 independent experiments.