Schematic diagram showing the reporter plasmid pRL-TKGFP-CMVE used in the flow cytometry-based barrier function assay (A) and the reporter plasmid pRL-TKGFP-CMVE-TKRFP used in the flow cytometry-based enhancer blocking assay (B). Abbreviations: 1.2 kb 5′HS4, 1.2-kb fragment of the chicken β-globin 5′HS4 insulator; GFP, enhanced GFP gene; RFP, DsRed.T4 gene; E, human CMV immediate early region enhancer; P, herpes simplex virus TK promoter.