ICTV Virus Taxonomy Profile: Sphaerolipoviridae 2023

Members of the family Sphaerolipoviridae have non-enveloped tailless icosahedral virions with a protein-rich internal lipid membrane. The genome is a linear double-stranded DNA of about 30 kbp with inverted terminal repeats and terminal proteins. The capsid has a pseudo triangulation T= 28 dextro symmetry and is built of two major capsid protein types. Spike complexes decorate fivefold vertices. Sphaerolipoviruses have a narrow host range and a lytic life cycle, infecting haloarchaea in the class Halobacteria (phylum Euryarchaeota). This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Sphaerolipoviridae, which is available at ictv.global/report/ sphaerolipoviridae.


VIRION
Sphaerolipoviruses have tailless icosahedral virions with an internal protein-rich membrane vesicle (Table 1; Fig. 1) [1][2][3][4][5].The virion is typically about 80 nm in diameter with major and minor capsid proteins, internal membrane proteins and vertex complex proteins (Fig. 1).The capsid has a pseudo T=28 dextro triangulation number [4].The two major capsid proteins (MCPs) VP4 and VP7 have a vertical single jelly-roll fold.The capsid lattice is built of pseudohexameric capsomers with either two or three towers (Fig. 1) made of VP4-VP4 homodimers and VP4-VP7 heterodimers [4].The vertices are occupied by penton proteins forming the binding position for the spike complex.Vertex complexes are either horn-shaped or propeller-shaped [4].MCPs, the major membrane protein, and the putative packaging

Abstract
Members of the family Sphaerolipoviridae have non-enveloped tailless icosahedral virions with a protein-rich internal lipid membrane.The genome is a linear double-stranded DNA of about 30 kbp with inverted terminal repeats and terminal proteins.The capsid has a pseudo triangulation T=28 dextro symmetry and is built of two major capsid protein types.Spike complexes decorate fivefold vertices.Sphaerolipoviruses have a narrow host range and a lytic life cycle, infecting haloarchaea in the class Halobacteria (phylum Euryarchaeota).This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Sphaerolipoviridae, which is available at ictv.global/report/ sphaerolipoviridae.ATPase are the most conserved structural proteins among sphaerolipoviruses [3,4].The lipids of the internal membrane vesicle are selectively acquired from host-cell membranes.Membrane vesicles are rich in virus-specific proteins.Major phospholipid species are phosphatidylglycerol, phosphatidylglycerophosphate methyl ester and phosphatidylglycerosulfate [3].

REPLICATION
Replication is probably protein-primed [5], but the genome does not encode a canonical DNA polymerase.The genome of SH1 virus has genes organized in seven major transcripts, some of which overlap [5].Six early transcripts encode structural genes, while one late transcript encodes proteins of unknown function.
Spaherolipoviruses originate from hypersaline environments, and their host range is limited to a few haloarchaeal strains belonging to the genera Haloarcula and Halorubrum [6].Sphaerolipoviruses bind to their hosts most probably by spike complexes at the virion vertices.Adsorption is relatively slow and the infection cycle is lytic, lasting 6-12 h [1][2][3].Several putative proviral regions related to sphaerolipoviruses are found in the chromosomes of halophilic archaea [6].

RESOURCES
Full ICTV Report on the family Sphaerolipoviridae: ictv.global/report/sphaerolipoviridae.