Adenovirus origin of DNA replication: sequence requirements for replication in vitro.

The initiation of adenovirus DNA takes place at the termini of the viral genome and requires the presence of specific nucleotide sequence elements. To define the sequence organization of the viral origin, we tested a large number of deletion, insertion, and base substitution mutants for their ability to support initiation and replication in vitro. The data demonstrate that the origin consists of at least three functionally distinct domains, A, B, and C. Domain A (nucleotides 1 to 18) contains the minimal sequence sufficient for origin function. Domains B (nucleotides 19 to 40) and C (nucleotides 41 to 51) contain accessory sequences that significantly increase the activity of the minimal origin. The presence of domain B increases the efficiency of initiation by more than 10-fold in vitro, and the presence of domains B and C increases the efficiency of initiation by more than 30-fold. Mutations that alter the distance between the minimal origin and the accessory domains by one or two base pairs dramatically decrease initiation efficiency. This critical spacing requirement suggests that there are specific interactions between the factors that recognize the two regions.