:Lipothrixviridae

The following genera and species are assigned to the family:

• Alphalipothrixvirus
• Betalipothrixvirus
• Deltalipothrixvirus

The family consists of three genera: Alphalipothrixvirus, Betalipothrixvirus, and Deltalipothrixvirus. Captovirus used to be in this family as the genus Gammalipothrixvirus, but now it is the only genus in the family Ungulaviridae.{{cite web | url=https://ictv.global/taxonomy | title=Current ICTV Taxonomy Release | ICTV }}Häring M, Vestergaard G, Brügger K, Rachel R, Garrett RA, Prangishvili D (2005) Structure and genome organization of AFV2, a novel archaeal lipothrixvirus with unusual terminal and core structures. J Bacteriol 187(11): 3855–3858 {{doi|10.1128/JB.187.11.3855-3858.2005}} They are classified into genera based on their genomic properties and on the diversity of their terminal appendages, which are involved in host cell recognition. The originally proposed genus Alphalipothrixvirus was renamed Alphatristromavirus and moved to family Tristromaviridae.{{cite journal |last1=Prangishvili |first1=D |last2=Rensen |first2=E |last3=Mochizuki |first3=T |last4=Krupovic |first4=M |last5=ICTV Report |first5=Consortium |title=ICTV Virus Taxonomy Profile: Tristromaviridae. |journal=The Journal of General Virology |date=February 2019 |volume=100 |issue=2 |pages=135–136 |doi=10.1099/jgv.0.001190 |pmid=30540248|doi-access=free }}{{cite web |title=ICTV Report Tristromaviridae |url=http://www.ictv.gobal/report/tristromaviridae}} In 2020, the genus Alphalipothrixvirus was recreated for classification of Sulfolobus filamentous virus 1{{cite journal |last1=Liu |first1=Y |last2=Osinski |first2=T |last3=Wang |first3=F |last4=Krupovic |first4=M |last5=Schouten |first5=S |last6=Kasson |first6=P |last7=Prangishvili |first7=D |last8=Egelman |first8=EH |title=Structural conservation in a membrane-enveloped filamentous virus infecting a hyperthermophilic acidophile. |journal=Nature Communications |date=2018 |volume=9 |issue=1 |pages=3360 |doi=10.1038/s41467-018-05684-6 |pmid=30135568|pmc=6105669 |bibcode=2018NatCo...9.3360L }} and Sulfolobales Beppu filamentous virus 2.{{cite journal |last1=Liu |first1=Y |last2=Brandt |first2=D |last3=Ishino |first3=S |last4=Ishino |first4=Y |last5=Koonin |first5=EV |last6=Kalinowski |first6=J |last7=Krupovic |first7=M |last8=Prangishvili |first8=D |title=New archaeal viruses discovered by metagenomic analysis of viral communities in enrichment cultures. |journal=Environmental Microbiology |date=2019 |volume=21 |issue=6 |pages=2002–2014 |doi=10.1111/1462-2920.14479 |pmid=30451355|bibcode=2019EnvMi..21.2002L |s2cid=53950297 |pmc=11128462 }}

In the genus Gammalipothrixvirus claw-like structures are found at either end of the virion.

Members of the Lipothrixviridae share structural and genomic characteristics with viruses from the Rudiviridae family, which contains non-enveloped rod-shaped viruses. Viruses from the two families have linear dsDNA genomes and share up to nine genes. In addition, the filamentous particles of rudiviruses and lipothrixviruses are built from structurally similar, homologous major capsid proteins. Due to these shared properties viruses from the two families are classified into an order Ligamenvirales.{{cite journal|title=A new proposed taxon for double-stranded DNA viruses, the order "Ligamenvirales"|journal=Arch Virol|year=2012|volume=157|issue=4|pages=791–795|doi=10.1007/s00705-012-1229-7|pmid=22270758|author=Prangishvili D, Krupovic M|doi-access=free}}

Members of the Ligamenvirales are structurally related to viruses of the family Tristromaviridae which, similar to lipothrixviruses, are enveloped and encode two paralogous major capsid proteins with the same fold as those of ligamenviruses.{{cite journal |last1=Wang |first1=Fengbin |last2=Baquero |first2=Diana P |last3=Su |first3=Zhangli |last4=Osinski |first4=Tomasz |last5=Prangishvili |first5=David |last6=Egelman |first6=Edward H |last7=Krupovic |first7=Mart |title=Structure of a filamentous virus uncovers familial ties within the archaeal virosphere |journal=Virus Evolution |date=2020 |volume=6 |issue=1 |pages=veaa023 |doi=10.1093/ve/veaa023 |pmid=32368353 |pmc=7189273 |url=}} Due to these structural similarities, order Ligamenvirales and family Tristromaviridae were proposed to be unified within a class 'Tokiviricetes' (toki means ‘thread’ in Georgian and viricetes is an official suffix for a virus class).

The viruses are enveloped and filamentous. The capsid varies considerably in length – 410–1950 nanometers (nm) – and is 24–38 nm in diameter. The envelope has a monolayer structure and includes di-phytanyl tetraethers lipids.{{cn|date=November 2022}}

From either end of the viron are protrusions extending from the core through the envelope. The capsid itself is elongated and exhibits helical symmetry. The core itself is helical.{{cn|date=November 2022}}

There are two major capsid proteins (MCP1 and MCP2). MCP1 and MCP2 form a heterodimer, which wraps around the linear dsDNA genome transforming it into A-form. Interaction between the genome and the MCPs leads to condensation of the genome into the virion superhelix.{{cite journal |last1=Kasson |first1=P |last2=DiMaio |first2=F |last3=Yu |first3=X |last4=Lucas-Staat |first4=S |last5=Krupovic |first5=M |last6=Schouten |first6=S |last7=Prangishvili |first7=D |last8=Egelman |first8=EH |title=Model for a novel membrane envelope in a filamentous hyperthermophilic virus. |journal=eLife |date=2017 |volume=6 |pages=e26268 |doi=10.7554/eLife.26268 |pmid=28639939|pmc=5517147 |doi-access=free }}{{cite journal |last1=Wang |first1=F |last2=Baquero |first2=DP |last3=Beltran |first3=LC |last4=Su |first4=Z |last5=Osinski |first5=T |last6=Zheng |first6=W |last7=Prangishvili |first7=D |last8=Krupovic |first8=M |last9=Egelman |first9=EH |title=Structures of filamentous viruses infecting hyperthermophilic archaea explain DNA stabilization in extreme environments. |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2020 |volume=117 |issue=33 |pages=19643–19652 |doi=10.1073/pnas.2011125117 |pmid=32759221|pmc=7443925 |doi-access=free |bibcode=2020PNAS..11719643W }} Genomes are linear, up to 40 kb in length.

Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption to the host cell. Acidianus filamentous virus 1 was found to bind to cellular pili-like appendages. DNA templated transcription is the method of transcription. Archaea serve as the natural host. Transmission routes are passive diffusion.

Virion assembly and egress have been studied in the case of Sulfolobus islandicus filamentous virus (SIFV). The 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.{{cite journal |last1=Baquero |first1=DP |last2=Gazi |first2=AD |last3=Sachse |first3=M |last4=Liu |first4=J |last5=Schmitt |first5=C |last6=Moya-Nilges |first6=M |last7=Schouten |first7=S |last8=Prangishvili |first8=D |last9=Krupovic |first9=M |title=A filamentous archaeal virus is enveloped inside the cell and released through pyramidal portals. |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2021 |volume=118 |issue=32 |pages=e2105540118 |doi=10.1073/pnas.2105540118 |pmid=34341107|pmc=8364153 |doi-access=free |bibcode=2021PNAS..11805540B }} All lipothrixviruses are likely to be lytic viruses. In the case of betalipothrixviruses and deltalipothrixviruses, virions are released through pyramidal portals, referred to as virus-associated pyramids (VAPs). The VAPs of SIFV have a hexagonal base (i.e., constructed from six triangular facets).

{{Reflist|2}}

• {{Commonscatinline|Lipothrixviridae}}
• [http://viralzone.expasy.org/all_by_species/143.html Viralzone: Lipothrixviridae]

{{Baltimore classification}}

{{Taxonbar|from=Q1468819}}

Category:Virus families