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Thaspiviridae: Taxonomy, Structure, Genome, and Replication !

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Taxonomic ClassificationStructural Characteristics

Taxonomic Classification

The Thaspiviridae family consists of spindle-shaped viruses classified as incertae sedis due to their uncertain taxonomic placement. The family contains a single genus, Nitmarvirus, which includes the species:

  • Nitmarvirus NSV1

These viruses specifically infect mesophilic ammonia-oxidizing archaea belonging to the genus Nitrosopumilus.

Structural Characteristics

The virions of Thaspiviridae exhibit spindle-shaped morphology with the following distinctive features:

  • Dimensions: Virions measure 64 ± 3 nm in diameter and 112 ± 6 nm in length.
  • Structural Details: A single pole of the virion is adorned with short fibers.
  • Similarity: Morphologically, these viruses resemble members of the families Fuselloviridae (infecting hyperthermophilic archaea) and Halspiviridae (infecting hyperhalophilic archaea).
genomic propertiesReplication Characteristics

genomic properties

Genome Structure:

  • The genome is a linear double-stranded DNA (dsDNA) molecule with a size of 27–29 kbp.
  • It contains 176 bp terminal inverted repeats (TIRs), a feature often associated with linear viral genomes.

Gene Content:

  • The genome is predicted to encode 48 genes.
  • Notably, most of these genes encode proteins that are unrelated to other known archaeal or bacterial viruses.

Key Enzymes:

  • A protein-primed family B DNA polymerase, which is also found in other archaeal viruses and mobile genetic elements with linear genomes, plays a critical role in viral replication.
  • The genome also encodes a proliferating cell nuclear antigen (PCNA), likely involved in DNA replication and repair processes.


Replication Characteristics

Replication Mode:

  • The virus exhibits non-lytic replication, allowing it to exit host cells without causing cell death.
  • It is classified as chronic, capable of persisting within the host organism indefinitely, with the potential for disease manifestation or latency.

Mechanisms of Replication:

  • Viral genome replication is presumed to rely on the virus-encoded protein-primed family B DNA polymerase, a mechanism similar to that of other archaeal viruses.
  • The PCNA protein encoded by the virus is likely a crucial factor in the viral replication process.