THE NFIII OCT-1 BINDING-SITE STIMULATES ADENOVIRUS DNA-REPLICATION INVIVO AND IS FUNCTIONALLY REDUNDANT WITH ADJACENT SEQUENCES/

The inverted terminal repeat (ITR) of adenovirus type 5 (Ad5) is 103 b p in length and contains the origin of DNA replication. Cellular trans cription factors NFI/CTF and NFIII/OCT-1 bind to sites within the ITR and participate in the initiation of viral DNA replication in vitro. T he ITR also contains multiple copies of two conserved sequence motifs that bind the cellular transcription factors SP1 and ATF. We have anal yzed a series of viruses that carry deletions at the left terminus of Ad5. A virus carrying a deletion of the NFIII/OCT-1, SP1, and ATF site s within the ITR (mutant dl309-44/107) was wild type for virus growth. However, the deletion of these elements in addition to sequences imme diately flanking the ITR (mutant dl309-44/195) resulted in a virus tha t grew poorly. The analysis of growth parameters of these and other mu tants demonstrate that the NFIII/OCT-1 and adjacent SP1 sites augment the accumulation of viral DNA following infection. The function of the se elements was most evident in coinfections with a wild-type virus, s uggesting that these sites enhance the ability of a limiting trans-act ing factor(s), that stimulates viral DNA replication, to interact with the ITR. The results of these analyses indicate functional redundancy between different transcription elements at the left terminus of the Ad5 genome and demonstrate that the NFIII/OCT-1 site and adjacent SP1 site, previously thought to be nonessential for adenovirus growth, pla y a role in viral DNA replication in vivo.