Molecular anatomy of Tupaia (tree shrew) adenovirus genome; evolution of viral genes and viral phylogeny.

Adenoviruses are globally spread and infect species in all five taxons of vertebrates. Outstanding attention is focused on adenoviruses because of their transformation potential, their possible usability as vectors in gene therapy and their applicability in studies dealing with, e.g. cell cycle control, DNA replication, transcription, splicing, virus-host interactions, apoptosis, and viral evolution. The accumulation of genetic data provides the basis for the increase of our knowledge about adenoviruses. The Tupaia adenovirus (TAV) infects members of the genus Tupaiidae that are frequently used as laboratory animals in behavior research dealing with questions about biological and molecular processes of stress in mammals, in neurobiological and physiological studies, and as model organisms for human hepatitis B and C virus infections. In the present study the TAV genome underwent an extensive analysis including determination of codon usage, CG depletion, gene content, gene arrangement, potential splice sites, and phylogeny. The TAV genome has a length of 33,501 bp with a G+C content of 49.96%. The genome termini show a strong CG depletion that could be due to methylation of these genome regions during the viral replication cycle. The analysis of the coding capacity of the complete TAV genome resulted in the identification of 109 open reading frames (ORFs), of which 38 were predicted to be real viral genes. TAV was classified within the genus Mastadenovirus characterized by typical gene content, arrangement, and homology values of 29 conserved ORFs. Phylogenetic trees show that TAV is part of a separate evolutionary lineage and no mastadenovirus species can be considered as the most related. In contrast to other mastadenoviruses a direct ancestor of TAV captured a DUT gene from its mammalian host, presumably controlling local dUTP levels during replication and enhance viral replication in non-dividing host tissues. Furthermore, TAV possesses a second DNA-binding protein gene, that is likely to play a role in the determination of the host range. In view of these data it is conceivable that TAV underwent evolutionary adaptations to its biological environment resulting in the formation of special genomic components that provided TAV with the ability to expand its host range during viral evolution.

Characterization of the complete genome of the Tupaia (tree shrew) adenovirus.

The members of the family Adenoviridae are widely spread among vertebrate host species and normally cause acute but innocuous infections. Special attention is focused on adenoviruses because of their ability to transform host cells, their possible application in vector technology, and their phylogeny. The primary structure of the genome of Tupaia adenovirus (TAV), which infects Tupaia spp. (tree shrew) was determined. Tree shrews are taxonomically assumed to be at the base of the phylogenetic tree of mammals and are frequently used as laboratory animals in neurological and behavior research. The TAV genome is 33,501 bp in length with a G+C content of 49.96% and has 166-bp inverted terminal repeats. Analysis of the complete nucleotide sequence resulted in the identification of 109 open reading frames (ORFs) with a coding capacity of at least 40 amino acid residues. Thirty-eight of them are predicted to encode viral proteins based on the presence of transcription and translation signals and sequence and positional conservation. Thirty viral ORFs were found to show significant similarities to known adenoviral genes, arranged into discrete early and late genome regions as they are known from mastadenoviruses. Analysis of the nucleotide content of the TAV genome revealed a significant CG dinucleotide depletion at the genome ends that suggests methylation of these genomic regions during the viral life cycle. Phylogenetic analysis of the viral gene products, including penton and hexon proteins, viral protease, terminal protein, protein VIII, DNA polymerase, protein IVa2, and 100,000-molecular-weight protein, revealed that the evolutionary lineage of TAV forms a separate branch within the phylogenetic tree of the Mastadenovirus genus.