''Betalipothrixvirus hveragerdiense'' (SIFV) is an

archaeal virus An archaeal virus is a virus that infects and replicates in archaea, a domain of unicellular, prokaryotic organisms. Archaeal viruses, like their hosts, are found worldwide, including in extreme environments inhospitable to most life such as ac ...

, classified in the family ''

Lipothrixviridae ''Lipothrixviridae'' is a family of viruses in the order '' Ligamenvirales''. Thermophilic archaea in the phylum Thermoproteota The Thermoproteota are prokaryotes that have been classified as a phylum (biology), phylum of the domain Archaea. ...

'' within the order ''

Ligamenvirales ''Ligamenvirales'' is an order of linear viruses that infect archaea of the phylum Thermoproteota (formerly Crenarchaeota) and have double-stranded DNA genomes. The order was proposed by David Prangishvili and Mart Krupovic in 2012 and subsequent ...

''. The virus infects hyperthermophilic and acidophilic archaeon '' Sulfolobus islandicus''. SIFV has a linear double-stranded DNA genome of 40,852 bp, which is the largest among characterized lipothrixviruses. The virions are enveloped filaments, nearly 2 micrometers in length. The nucleocapsid is formed from two paralogous major capsid proteins, which tightly wrap around the dsDNA genome; notably, dehydration of the genomic DNA by the major capsid proteins transforms the B-form DNA into A-form DNA.

Life cycle

SIFV virions assemble inside the cell. Binding of the major capsid protein dimers to the linear dsDNA genome lead to the assembly of nucleocapsids, which are subsequently enveloped intracellularly through an unknown mechanism. SIFV and probably other lipothrixviruses are lytic viruses. Virion release takes place through pyramidal portals, referred to as virus-associated pyramids (VAPs). Unlike in the case of some other archaeal viruses (e.g., rudiviruses and turriviruses), the SIFV VAPs have a hexagonal base (i.e., constructed from six triangular facets). The VAPs can be as large as 220 nm at the base and are constructed from a single SIFV-encoded protein of 89 aa. Expression of this protein in ''

E. coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escherichia'' that is commonly foun ...

'' leads to VAP formation in the inner bacterial membrane.

References

Archaeal viruses Ligamenvirales {{virus-stub