Characterization of the genome of a vaccine strain of canine adenovirus type 1

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Abstract
Restriction endonuclease cleavage maps have been constructed for the genome of a canine adenovirus type 1 (CAV-1) vaccine strain (CLL; Connaught Laboratories, Ltd., Willowdale, Ontario). Restriction enzyme analyses were also carried out on CAV-1 (CLL) genomes isolated from viral stocks over 8 serial passages in a dog kidney cell line (DK 6722). The right hand 20% of the genome became more heterogeneous in size with increasing passage in DK 6722 cells due to deletions up to 3–4 kb, whereas the left terminal region was stable throughout these passages. A comparative study of CAV-1(CLL) and a virulent strain of CAV-1, Glaxo, revealed that the genome of CAV-1(CLL) was the shorter, by about 480 bp, within the region covering 0.83–0.91 map units. By virtue of its location within the genome and its dispensable nature for viral growth, this region would appear to encompass a genetic sequence corresponding to the E3 region of human adenoviruses. In terms of viral attenuation, the possible importance of the observed differences between CAV-1(CLL) and CAV-1(Glaxo) is discussed.