The putative hexon gene of bovine adenovirus type 4 (BAV-4), encoding 910 amino acid residues, has been identified and sequenced. A characteristic codon usage biased towards the use of AT-rich triplets was observed. Comparative analysis with other hexon sequences detected a high level of amino acid identity in the regions corresponding to the pedestals of the hexon. Substitutions, insertions and deletions were identified mainly in the variable regions forming the loops which are exposed on the outer surface of the virion. In these variable regions, BAV-4 shared similarity only with egg drop syndrome (EDS) virus and ovine adenovirus isolate 287 (OAV287). The close relationship of these viruses was also demonstrated by phylogenetic analysis of the hexon gene. In addition to the two groups of the Mastadenovirus and Aviadenovirus genera, a third cluster appeared comprising BAV-4, OAV287 and EDS virus.
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