Transactivation mediated by the 12-bp enhancer is copy number dependent and orientation independent. (A) The double-stranded oligonucleotide, its copy number and orientation (forward, reverse) with respect to the minimal promoter in RCBX64 (–) is indicated. The average activity of each reporter plasmid in H4IIEC3 cells relative to that of RCBX64 is shown, n = 3. Error bars indicate SD. (B) The effect of the 12-bp sequence on a heterologous viral promoter in H4IIEC3 cells was analyzed. WT indicates 1 copy of the wild type 12-bp sequence in the forward direction; Mut, 1 copy of mutant oligonucleotide B in the forward orientation. The average activities of these reporter plasmids are shown relative to that of the parental minimal SV40 viral promoter vector (–), n = 3.