From small hosts come big viruses: the complete genome of a second Ostreococcus tauri virus, OtV-1

Ostreococcus tauri virus (OtV-1) is a large double-stranded DNA virus and a prospective member of the family Phycodnaviridae, genus Prasinovirus. OtV-1 infects the unicellular marine green alga O. tauri, the smallest known free-living eukaryote. Here we present the 191 761 base pair genome sequence of OtV-1, which has 232 putative protein-encoding and 4 tRNA-encoding genes. Approximately 31% of the viral gene products exhibit a similarity to proteins of known functions in public databases. These include a variety of unexpected genes, for example, a PhoH-like protein, a N-myristoyltransferase, a 3-dehydroquinate synthase, a number of glycosyltransferases and methyltransferases, a prolyl 4-hydroxylase, 6-phosphofructokinase and a total of 8 capsid proteins. A total of 11 predicted genes share homology with genes found in the Ostreococcus host genome. In addition, an intein was identified in the DNA polymerase gene of OtV-1. This is the first report of an intein in the genome of a virus that infects O. tauri. Fifteen core genes common to nuclear-cytoplasmic large dsDNA virus (NCLDV) genomes were identified in the OtV-1 genome. This new sequence data may help to redefine the classification of the core genes of these viruses and shed new light on their evolutionary history.