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Type Species |
(SSV1) |
Virions are lemon-shaped, slightly flexible in appearance with short tail fibers attached to one pole. Virions are 60 
100 nm in size; a small fraction of the Sulfolobus virus 1 (SSV1) population (up to 1%) is larger with a particle length of about 300 nm. The virion envelope consists of host lipids and of two virus-encoded proteins; a third protein is DNA-associated (Fig. 1).
Physicochemical and Physical Properties
Virion buoyant density in CsCl is 1.24 g/cm3. The particles are stable at up to 85°C and are insensitive to urea and ether. Low pH (below 5) reduces viability due to degradation of the DNA; virions are sensitive to high pH (above 11) and trichloromethane.
Virions contain circular, positively supercoiled dsDNA, of 15,465 bp in size. Virion DNA is associated with polyamines and a virus-coded basic protein. The nucleic acid sequence has been completely determined and the data are available from EMBL/GenBank.
Two basic proteins (VP1 and VP3) are constituents of the virion envelope. They consist of 73 and 92 amino acid residues as deduced from the nucleic acid sequence. A very basic protein (VP2, 74 aa) is attached to the viral DNA. The genes encoding these three structural proteins are closely linked on the SSV1 genome, in the order VP1, VP3, and VP2. The second largest ORF of SSV1 (ORF d335, 335 aa) shows sequence homology to the integrase family of site-specific recombinases. This protein has been expressed in E. coli and recombines DNA fragments sequence-specifically in vitro.
10% of the SSV1 envelope consists of host lipids.
None reported.
Genome Organization and Replication
The SSV1 genome is present in the cells as cccDNA and also site-specifically integrated into a tRNA gene of the host chromosome. The integrated copy is flanked by a 44 bp direct repeat (attachment core) that occurs once in the circular SSV1 DNA. Upon integration, ORF d335 is disrupted. Eleven transcripts, initiated from 7 promoters, cover the SSV1 genome. UV-irradiation is a stimulus for virus production and the particles are released without evident lysis of the host cells. A small transcript (Tind) is strongly induced upon induction. Particles are probably assembled at the cell membrane, since no virus particles have been observed in host cells. See Fig. 2.
Host range is limited to two extremely thermophilic archaea, Sulfolobus shibatae and Sulfolobus isolates P1 and P2. Few phage particles are produced in cultures of lysogens. UV-irradiation strongly induces phage production without evident lysis of the host.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
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Sulfolobus virus 1 |
[XO7234] |
(SSV-1) |
Tentative Species in the Genus
None reported.
Unassigned Viruses in the Family
None reported.
Phylogenetic Relationships within the Family
Not applicable.
None reported.
Fusello: from Latin fusello, “little spindle”.
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