Figure 4. Dose-dependent activation of the PLK1 promoter and 5′ deletion mutants by p68. (A) The full-length PLK1 promoter or its deletion derivatives were transfected individually into H1299 cells that lack functional p53, together with increasing amounts of p68, and assayed for luciferase activity 24 h post-transfection with empty pGL3 vector as control. The results presented are mean ± SD of 3 independent experiments, each performed in triplicate. (B) Western blot showing increasing amounts of Myc-tagged p68 expressed in H1299 cells, with actin serving as loading control. Similar results were obtained whether p68 was Myc-tagged or un-tagged.