Transcription in the reverse orientation at either terminus of the adenovirus type 5 genome

The right terminus of the adenovirus type 5 (Ad5) genome, which contained the early-region 4 (E4) promoter, was capable of initiating transcription in the reverse orientation in in vitro and in vivo assays. Multiple cis-acting elements, required for original-oriented transcription, were also important for reverse-oriented transcription except for the original TATA box. We constructed a plasmid in which the E4 promoter region was linked to the chloramphenicol acetyltransferase gene in the original orientation and linked to the lacZ gene in the reverse orientation and tested the ability of a co-transfected E1A gene to stimulate transcription in both orientations. Activities of transcription in both orientations were stimulated 6- to 10-fold in this assay. More than one cis-acting element was necessary for the stimulation. The region between -39 and -177 was necessary for the E1A-mediated trans-activation of transcription in both orientations, indicating that the region functioned in a bidirectional manner. The activity of transcription in the reverse orientation was similarly detected at the left terminus of the Ad genome and the activity was stimulated several-fold by E1A gene products.