Redundant elements in the adenovirus type 5 inverted terminal repeat promote bidirectional transcriptionin Vitro and are important for virus growthin Vivo

The adenovirus inverted terminal repeat (ITR) contains a number ofcis-acting elements that are involved in the initiation of viral DNA replication, as well as multiple binding motifs for the cellular transcription factors SP1 and ATF. In this study, we utilized a Hela cell transcription extract to demonstrate that the adenovirus type 5 ITR promotes bidirectional transcriptionin vitro. Primer extension analyses demonstrated that the ITR directed transcription at initiation sites both within the terminal repeat and at fixed distances outside of the ITR. The ITR also strongly stimulated transcription at the early region 1A (E1A) initiation site when it was situated immediately upstream of the E1A TATA {ballot box} region. Deletion and point mutational analyses demonstrated that two distinctcis-acting elements were involved in these ITR-dependent transcriptional activitiesin vitro. Cellular transcription factors SP1 and ATF were previously shown to bind to these two regions. Analysis of viral mutantsin vivo demonstrated that the NFIII/OCT-1 binding site and a conserved ATF motif were important for efficient viral growth. Regulatory elements in the ITR flanking region were found to functionally substitute for these sites.