DNA virus
Third, the RNA polymerase terminates transcription upon reaching a specific signal, such as a polyadenylation site.
[5] A rolling circle mechanism that produces linear strands while progressing in a loop around the circular genome is also common.
However, because the genome is single-stranded, it is first made into a double-stranded form by a DNA polymerase upon entering a host cell.
The double-stranded form of ssDNA viruses may be produced either directly after entry into a cell or as a consequence of replication of the viral genome.
[15] Parvoviruses, as previously mentioned, may package either the positive or negative sense strand into virions.
Within each realm, viruses are grouped together based on shared characteristics that are highly conserved over time.
Duplodnaviria contains dsDNA viruses that encode a major capsid protein (MCP) that has the HK97 fold.
[11] Duplodnaviria is a very ancient realm, perhaps predating the last universal common ancestor (LUCA) of cellular life.
[22][23] Tailed bacteriophages are ubiquitous worldwide,[24] important in marine ecology,[25] and the subject of much research.
[26] Herpesviruses are known to cause a variety of epithelial diseases, including herpes simplex, chickenpox and shingles, and Kaposi's sarcoma.
The prototypical members of the realm are called CRESS-DNA viruses and have circular ssDNA genomes.
[30] Viruses in Monodnaviria appear to have emerged on multiple occasions from archaeal and bacterial plasmids, a type of extra-chromosomal DNA molecule that self-replicates inside its host.
[30][31] CRESS-DNA viruses include three kingdoms that infect prokaryotes: Loebvirae, Sangervirae, and Trapavirae.
[30] Eukaryotic monodnaviruses are associated with many diseases, and they include papillomaviruses and polyomaviruses, which cause many cancers,[32][33] and geminiviruses, which infect many economically important crops.
[37] Poxviruses have been highly prominent in the history of modern medicine, especially Variola virus, which caused smallpox.
