Editing DNA virus (section)

===Single-stranded DNA viruses===
[[File:Canines_Parvovirus.jpg|thumb|The [[canine parvovirus]] is an ssDNA virus.]]
The second Baltimore group of DNA viruses are those that have a single-stranded DNA genome. ssDNA viruses have the same manner of transcription as dsDNA viruses. 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. mRNA is then synthesized from the double-stranded form. 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.<ref name=ssdna >{{cite web|title=ssDNA Rolling circle|url=https://viralzone.expasy.org/1941|website=ViralZone|publisher=Swiss Institute of Bioinformatics|access-date=24 September 2020}}</ref><ref name=hairpin >{{cite web|title=Rolling hairpin replication|url=https://viralzone.expasy.org/2656|website=ViralZone|publisher=Swiss Institute of Bioinformatics|access-date=24 September 2020}}</ref> Eukaryotic ssDNA viruses are replicated in the nucleus.<ref name=cann122 /><ref name=fermin40 >[[#fermin|Fermin 2018]], pp.&nbsp;40–41</ref>

Most ssDNA viruses contain circular genomes that are replicated via [[rolling circle replication]] (RCR). ssDNA RCR is initiated by an [[endonuclease]] that bonds to and cleaves the positive strand, allowing a DNA polymerase to use the negative strand as a template for replication. Replication progresses in a loop around the genome by means of extending the 3'-end of the positive strand, displacing the prior positive strand, and the endonuclease cleaves the positive strand again to create a standalone genome that is [[Ligation (molecular biology)|ligated]] into a circular loop. The new ssDNA may be packaged into virions or replicated by a DNA polymerase to form a double-stranded form for transcription or continuation of the replication cycle.<ref name=ssdna /><ref name=rampersad61 >[[#rampersad|Rampersad 2018]], pp.&nbsp;61–62</ref>

[[Parvovirus]]es contain linear ssDNA genomes that are replicated via [[rolling hairpin replication]] (RHR), which is similar to RCR. Parvovirus genomes have [[Stem-loop|hairpin loops]] at each end of the genome that repeatedly unfold and refold during replication to change the direction of DNA synthesis to move back and forth along the genome, producing numerous copies of the genome in a continuous process. Individual genomes are then excised from this molecule by the viral endonuclease. For parvoviruses, either the [[Sense (molecular biology)|positive or negative sense]] strand may be packaged into capsids, varying from virus to virus.<ref name=rampersad61 /><ref>{{cite book |vauthors=Kerr J, Cotmore S, Bloom ME |date=25 November 2005 |title=Parvoviruses |publisher=CRC Press |pages=171–185 |isbn=9781444114782}}</ref>

Nearly all ssDNA viruses have positive sense genomes, but a few exceptions and peculiarities exist. The family ''[[Anelloviridae]]'' is the only ssDNA family whose members have negative sense genomes, which are circular.<ref name=fermin40 /> Parvoviruses, as previously mentioned, may package either the positive or negative sense strand into virions.<ref name=hairpin /> Lastly, [[Bidensovirus|bidnavirus]]es package both the positive and negative linear strands.<ref name=fermin40 /><ref name=bidna >{{cite web|title=Bidnaviridae|url=https://viralzone.expasy.org/2957|website=ViralZone|publisher=Swiss Institute of Bioinformatics|access-date=24 September 2020}}</ref>