Multiple reiteration of a 40-bp nucleotide sequence in the inverted terminal repeat of the genome of a canine adenovirus.

The DNA of a vaccine strain of canine adenovirus type 1 [ICHV vaccine; Connaught Laboratories, Ltd.; CAV-1(CLL)] has been cloned in plasmid pAT153 in the form of subgenomic BamHI digestion fragments. Analysis of the nucleotide sequences of cloned terminal fragments has revealed an inverted terminal repeat (ITR) with a minimum length of 198 nucleotides, including a tandem reiteration of the 40-bp nucleotide sequence from positions 14 to 53. The ITRs had the 5'-CATCATCAAT ... sequence typical of adenoviruses and the highly conserved sequence ATAATATAC (nucleotides 9-17) of human strains. Additionally, one BamHI A clone (left terminus) contained three sequential copies of the 40-bp sequence, and two BamHI C clones (right terminus) contained at least seven. These did not appear to be artifacts of cloning, since evidence was obtained that the multiple reiterations also occurred in DNA isolated from intact virus. By analogy with human adenoviruses, the repetitive sequence in the CAV-1(CLL) genome encompasses the entire nuclear factor I (NFI) binding site of the origin of DNA replication. Additionally, the 40-bp nucleotide sequence was found to contain the sequence AGG(N)4GCCTAA (nucleotides 27-39), which closely resembles the concensus sequence of the human adenovirus NFI binding site [TGG(N)6-7GCCAA; nucleotides 25-38]. It appears, therefore, that the Connaught CAV-1 vaccine contains reiterated copies of an essential part of the adenoviral origin of DNA replication. A mechanism is proposed for the generation of multiple reiterations of sequences in the right ITR, given an initial single tandem repeat in the left ITR.