Functional interactions of the simian virus 40 core origin of replication with flanking regulatory sequences

We constructed a matched set of plasmids to investigate the interactions of essential core sequences of the simian virus 40 replication origin with flanking regulatory sequences. Deletions of either T-antigen-binding region I or the 21-base-pair repeated promoter elements reduced replication to 50 to 70% of wild-type levels. The simultaneous deletion of both regions decreased replication to less than 5% of wild-type levels. Thus, the double deletion greatly amplified the defects of the single deletions. We conclude that region I and the 21-base-pair repeats have related rather than independent functions in DNA synthesis. Insertion of a synthetic region I or the adenovirus 2 major late promoter at the late side of isolated core sequences in place of the 21-base-pair repeats failed to restore replication. In contrast, insertion of a single 72-base-pair enhancer element stimulated replication of the core origin more than fivefold. Thus, three distinct regulatory elements appear to facilitate core DNA replication by related mechanisms. Flanking sequences have only a small direct effect on T-antigen binding to naked core DNA. Possible mechanisms of action include the regulation of transcription or of chromatin structure.