Portogloboviridae
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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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.
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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.
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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.