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Portogloboviridae

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Portogloboviridae is a proposed family of dsDNA viruses infecting archaea, currently classified as incertae sedis by the ICTV. These viruses are considered evolutionary significant as they may represent a primordial lineage within the Varidnaviria realm.

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1

Classification and General Characteristics  

Phylogenetic Position: Related to Helvetiavirae, they are considered potential representatives of an ancestor common to viruses within the Varidnaviria realm.

Virion Structure:

  • Capsid: Icosahedral, surrounded by an envelope.
  • Genome: Circular dsDNA of approximately 20,000 base pairs, densely packed with numerous short genes.
  • Size: Approximately 83-87 nm in diameter.

2

 Replication Cycle and Evolutionary Significance

  • Replication Cycle: Chronic infection without a lytic cycle. The virus enters the host cell and replicates continuously.
  • Evolutionary Significance:
    • Relics of LUCA: Portogloboviridae and Halopanivirales are believed to have infected the Last Universal Common Ancestor (LUCA) or even predated its existence.
    • Conservation of Ancestral Features: Capsid proteins, particularly the single jelly roll (SJR) protein, appear to have retained ancestral characteristics, making them valuable models for studying the origin of Varidnaviria.

3

 Perspectives and Open Questions

  • Taxonomic Position: The classification of Portogloboviridae remains to be clarified. Further phylogenetic analyses may allow for more precise placement within the Varidnaviria realm.
  • Origin and Evolution: Studying these viruses could shed light on the origin of dsDNA viruses and the evolution of early biological systems.
  • Ecological Role: The ecological role of Portogloboviridae in microbial ecosystems remains largely unknown.