title: HCIV-1 and Other Tailless Icosahedral Internal Membrane-Containing Viruses of the Family Sphaerolipoviridae.
abstract: Members of the virus familySphaerolipoviridaeinclude both archaeal viruses and bacteriophages that possess a tailless icosahedral capsid with an internal membrane. The generaAlpha-andBetasphaerolipoviruscomprise viruses that infect halophilic euryarchaea, whereas viruses of thermophilicThermusbacteria belong to the genusGammasphaerolipovirus. Both sequence-based and structural clustering of the major capsid proteins and ATPases of sphaerolipoviruses yield three distinct clades corresponding to these three genera. Conserved virion architectural principles observed in sphaerolipoviruses suggest that these viruses belong to the PRD1-adenovirus structural lineage. Here we focus on archaeal alphasphaerolipoviruses and their related putative proviruses. The highest sequence similarities among alphasphaerolipoviruses are observed in the core structural elements of their virions: the two major capsid proteins, the major membrane protein, and a putative packaging ATPase. A recently described tailless icosahedral haloarchaeal virus,Haloarcula californiaeicosahedral virus 1 (HCIV-1), has a double-stranded DNA genome and an internal membrane lining the capsid. HCIV-1 shares significant similarities with the other tailless icosahedral internal membrane-containing haloarchaeal viruses of the familySphaerolipoviridae. The proposal to include a new virus species,Haloarcula virus HCIV1, into the genusAlphasphaerolipoviruswas submitted to the International Committee on Taxonomy of Viruses (ICTV) in 2016.
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. tatiana.demina@helsinki.fi.
authors.forename: Tatiana A
authors.initials: TA
authors.lastname: Demina
authors.affiliation: Department of Food and Environmental Sciences, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. maija.pietila@helsinki.fi.
authors.forename: Maija K
authors.initials: MK
authors.lastname: Pietilä
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. julija.svirskaite@helsinki.fi.
authors.forename: Julija
authors.initials: J
authors.lastname: Svirskaitė
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. janne.ravantti@helsinki.fi.
authors.forename: Janne J
authors.initials: JJ
authors.lastname: Ravantti
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. nina.atanasova@helsinki.fi.
authors.forename: Nina S
authors.initials: NS
authors.lastname: Atanasova
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. dennis.bamford@helsinki.fi.
authors.forename: Dennis H
authors.initials: DH
authors.lastname: Bamford
authors.affiliation: Department of Biosciences and Institute of Biotechnology, Viikinkaari 9, FIN-00014, University of Helsinki, Helsinki, Finland. hanna.oksanen@helsinki.fi.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Oksanen
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics; D001105:Archaea / Q000821:virology; D023641:Archaeal Viruses / Q000145:classification* / Q000235:genetics / Q000648:ultrastructure*; D001435:Bacteriophages / Q000145:classification* / Q000235:genetics / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000235:genetics; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013824:Thermus / Q000821:virology; D014771:Virion / Q000648:ultrastructure*
chemical_list: D036022:Capsid Proteins; D000251:Adenosine Triphosphatases
keywords: Alphasphaerolipovirus; International Committee on Taxonomy of Viruses; Sphaerolipoviridae; archaeal virus; halophilic archaea; halovirus; membrane virus; structure-based viral lineage; tailless icosahedral virus; virus classification