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Review
. 2019 Mar;30(1):3-12.
doi: 10.1007/s13337-019-00519-4. Epub 2019 Apr 19.

ssDNA Viruses: Key Players in Global Virome

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Free PMC article
Review

ssDNA Viruses: Key Players in Global Virome

V G Malathi et al. Virusdisease. .
Free PMC article

Abstract

Single-stranded (ss)DNA viruses are extremely widespread, infect diverse hosts from all three domains of life and include important pathogens. Most ssDNA viruses possess small genomes that replicate by the rolling-circle-like mechanism initiated by a distinct virus-encoded endonuclease. High throughput genome sequencing and improved bioinformatics tools have yielded vast information on presence of ssDNA viruses in diverse habitats. The simple genome of ssDNA viruses have high propensity to undergo mutation and recombination often emerging as threat to human civilization. Interestingly their genome is found embedded in fossils dating back to million years. The unusual evolutionary history of ssDNA viruses reveal evidences of horizontal gene transfer, sometimes between different species and genera.

Keywords: CRESS viruses; Rolling circle replication; ssDNA.

Figures

Fig. 1
Fig. 1
Classification of ssDNA viruses into families with progress of time
Fig. 2
Fig. 2
Schematic representation of rolling circle replication (RCR) in circular ssDNA viruses. The encapsidated ssDNA released into host cell enters nucleus and is converted to dsDNA by host enzymes. Viral encoded Rep binds to dsDNA at iteron sequences and creates nick at nonanucleotide sequences to generate 3′ OH end. Rep is covalently bound to 5′ PO4 end. Host DNA polymerase synthesizes the virion sense strand using negative strand as template. As new strand is synthesized, old strand is displaced. When replication is completed Rep joins the nicks and releases initial strand from the replication complex
Fig. 3
Fig. 3
Schematic representation of rolling hairpin replication (RHR). Upon infection of host cell, 3′ end of the linear ssDNA serves as primer and host enzymes convert ssDNA to ds DNA. Replication is initiated by viral endonuclease NS1 which creates nicks between coding region and hairpin at 3′ region. New strand is synthesized by host DNA polymerase. Instead of simply ending at this point, the replication complex switches from the parental strand to the identical sequence on the newly synthesized strand and replication continues to produce a dsDNA molecule with paired hairpins at one end. This process then continues back and forth producing head to head and tail to tail, genomic concatemers within which the palindromic genome ends are replicated half as frequently as the coding regions. New single stranded breaks are introduced at the replication origins of these dsDNA molecules (by NS1), which result in the formation of new replication forks that, starting with the replication of the palindromic ends, displace ssDNA strands that are ready for packaging. Adapted from Martin et al. [40]

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