Sequence of Ovine Adenovirus Homologs for 100K Hexon Assembly, 33K, pVIII, and Fiber Genes: Early Region E3 Is Not in the Expected Location

AbstractOvine adenovirus OAV287 was previously isolated from sheep in Western Australia. As a first step in characterizing the genome of this virus we have determined the sequence of its genome between map units 65 and 81. This region was expected to contain the nonessential E3 region which, in other adenoviruses, lies between the genes encoding the pVIII and fiber proteins, although its size and complexity varies. OAV287 genes coding for the hexon assembly, 33K, pVIII, and fiber proteins were identified by their homologies with human Ad2. These genes lie in the same relative positions in the OAV287 genome, but the intergenic region between the pVIII and the fiber genes is only 197 nucleotides and these appear to be incapable of ceding for any protein. Thus, the ovine adenovirus E3 region is not present in the expected location. In addition, using cDNA synthesis, PCR amplification, and nucleotide sequencing we determined the location of splice junctions and transcription termination signals in mRNA species encoding these proteins. This showed that a family of variably spliced L4 RNAs is produced and that the region between the pVIII and the fiber genes contains several signals for RNA synthesis and processing. As the E3 region in human adenoviruses is nonessential for replication, in many instances it has been replaced with foreign DNA during the construction of recombinants. Because of this unexpected difference in the organization of the OAV287 genome further experimentation will be required to determine whether potential vaccine recombinants can be constructed for this adenovirus by making insertions into the pVIII/fiber intergenic region

Characterisation of Australian ovine adenovirus isolates

We have characterised two groups of adenoviruses isolated from sheep in Australia. Restriction endonuclease maps for enzymes BamHI, ClaI, SalI, SmaI and SphI have been determined for the genome of ovine adenoviruses related to bovine adenovirus serotype 7 (BAV 7) from sheep in Western Australia. Although previously serotyped as BAV 7 these isolates are different from bovine isolates of BAV 7 based on comparison with published restriction endonuclease profiles and maps of BAV 7 cattle isolates. Additional adenovirus isolates obtained from Victorian sheep have been serotyped as ovine adenovirus type 5 (OAV 5). On the basis of restriction endonuclease analysis these viruses are different from the sheep BAV 7 isolates. Following infection of sheep with ovine BAV 7 and OAV 5 isolates, virus was recovered from nasal and rectal swabs for several days. Antibodies detected by ELISA and serum neutralisation tests (SN) developed by 15 days after infection. Virus also spread from the infected sheep to an incontact control and one of ten sheep purchased for infection studies had SN antibodies to BAV 7 suggesting that BAV 7-like viruses naturally infect sheep in Victoria and Western Australia. With further development, these ovine adenoviruses may be suitable as vectors for the delivery of vaccine antigens to sheep and cattle