Comparison of the activities of the HHV-6 MIE promoter and CMV promoter. (A) The HHV-6 genome is a double-stranded DNA molecule of approximately 160 kbp, and is composed of a single long unique sequence (U) flanked by identical direct repeats (DRL and DRR). IE1 maps to open reading frames U90 and U89. The HHV-6 MIE promoter of 971 bp, located upstream of exon 1 of IE1, was amplified by PCR from the HHV-6B strain HST genome. Bases are numbered starting with the transcriptional start site for the IE1 gene. (B) The HHV-6 MIE promoter and CMV promoter were subcloned into the pGL3-basic plasmid, and the resultant plasmids were transfected into various cell lines (Jurkat, Molt-3, SupT1, MRC-5, MeWo, and U373 cells). At 24-hr post-transfection, the cells were harvested and subjected to the luciferase activity assay. The mean fold-activity relative to that of blank pGL3-basic plasmid-transfected cells and standard deviation for three independent experiments were plotted.