Adomaviruses: an emerging virus family provides insights into DNA virus evolution

Diverse eukaryotic dsDNA viruses, including adenoviruses, are thought to have evolved from bacteriophages of the family Tectiviridae. The evolutionary relationship of the small circular dsDNA tumor viruses of the families Papillomaviridae and Polyomaviridae to other DNA virus families remains uncertain. Metagenomic surveys of fish reveal 5 previously unknown circular dsDNA viruses that could become founding members of a distinct viral family. These viruses encode predicted superfamily 3 helicases that are related to the replicative helicases of polyomaviruses and papillomaviruses. Additionally, the new viruses encode a gene cluster coding for homologs of adenovirus-like maturation proteases and putative homologs of adenovirus major and minor capsid proteins. We show that these predicted capsid protein are indeed incorporated into the adomavirus virions. Such combination of genes from unrelated virus families is unprecedented among known DNA viruses. We propose the name Adomaviridae for this emerging virus family.