A, schematic representation of pHrD-IRES-Luc. A segment of the rRNA gene (−410 to +314 bp with respect to the transcriptional start site) was amplified using corresponding oligonucleotides and was cloned into modified pGL3-basic vector to generate pHrD-IRES-Luc (for details, see “Materials and Methods”). B and C, luciferase activity driven by pHrD-IRES-Luc is directed by pol I. Human rRNA promoter was methylated by M.HhaI or mock-methylated and ligated to pIRES-Luc to generate pHrD-IRES-Luc. The mock-methylated or methylated plasmid (500 ng) along with the internal control, pRLTK (50 ng), was transfected into HepG2 or Hepa cells by the calcium phosphate-DNA precipitation method. pRL-TK was used as internal control to measure transfection efficiency. After 24 h, both firefly and Renilla luciferase activity was measured using the Dual Luciferase Assay kit (Promega). Table B represents the firefly (RLU1) and Renilla (RLU2) luciferase activities and their ratios among different transfectants. C, graphical representation of the data.