Spleen necrosis virus A strain of

Reticuloendotheliosis virus.

spliceosome A multicomponent ribonucle-oprotein complex that carries out the splicing of RNA.

Guthrie C (1994) Harvey Lect 90, 59

splice sites The sites at which the intron is excised. The 5' splice site is adjacent to the GU end of the donor junction. The 3' splice site is adjacent to the AG end of the acceptor junction.

splicing Ligation of non-contiguous cleaved portions of an RNA molecule to remove introns from precursor RNA transcripts and produce functional mRNA. Originally discovered from work on adenovirus mRNA synthesis. Now known to be a common feature of mRNA production in eukaryotic cells. Functional mRNA in eukaryotic cells can be made up of spliced transcripts originating from widely separated regions of the DNA. The sequences of DNA, transcripts of which are present in mRNA, are termed 'exons' (expressed regions); the intervening DNA sequences, transcripts of which are removed by splicing, are termed 'introns'. Plays an important role in the expression of virus genomes whose replication involves the cell nucleus, such as influenza virus, retroviruses and several DNA viruses.

Darnell JE (1978) Science 202, 1257 Sharp PA (1994) Cell 77, 805

split vaccines Vaccines prepared from disrupted virus particles and purified to remove the toxic fraction of viral proteins which may cause side-effects. This permits the injection of a larger dose of the useful antigen.

Spondweni virus (SPOV) A strain of Zika virus in the genus Flavivirus. Isolated from culicine mosquitoes in S Africa,

Squirrel fibroma virus (SQFV)

Nigeria, Mozambique and Cameroon. Can cause a febrile illness with hepatitis in humans. Antibodies present in cattle, sheep and goats, in which it causes disease.

spongiform encephalopathy agents Prions causing scrapie, kuru, bovine spongiform encephalopathy, transmissible mink encephalopathy, Creutzfeldt-Jakob disease and related neurological disorders with a common pathological picture and progressive course to death. There is spongiform degeneration of the brain but absence of inflammatory reaction. They are caused by prions, self-replicating cellular protein isoforms that are not true viruses, as they contain no detectable nucleic acid. See prion. Synonym: subacute spongiform enceph-alopathy viruses.

Prusiner SB (editor) (1999) Prion Biology and Diseases. Cold Spring Harbor Laboratory Monograph 38, New York: Cold Spring Harbor Laboratory Press spongothymidine (Ara T) 1-P-d-Arabino-furanosylthymidine. A nucleoside antibiotic isolated from the sponge, Cryptotethia crypta. A selective inhibitor of Human herpesviruses 1 and 2.

spongouridine (Ara U) 1-P-d-Arabino-furanosyluracil. A nucleoside antibiotic isolated from the sponge, Cryptotethia crypta.

spontaneous mutant A mutation that arises naturally during virus replication.

sporadic infections Virus infections that occur at low frequency and in a seemingly unconnected way.

spring viremia of carp virus (SVCV) A tentative species in the genus Vesiculovirus. Causes disease and death in fish farms in the USA and Europe. Primarily a pathogen of carp but can infect pike. Replicates in FHM cells, most rapidly at 20-22°C, but can replicate at 31°C. Antigenically related to swim-bladder inflammation virus. The disease erupts in the spring, and both adults and young fish are killed by the infection which results in hemorrhage of the internal organs, including the swim-bladder. Lethargy, loss of balance and aimless swimming are clinical signs of the disease. Synonyms: infectious dropsy of carp virus; rhabdovirus carpio.

Bucke D and Finlay J (1979) Vet Rec 104, 69 Roy P and Clewley JP (1978) J Virol 25, 912

Spumavirinae An old name for a subfamily in the family Retroviridae that no longer exists.

Spumavirus (Latin: spuma = foam) A genus of the family Retroviridae. Usually cause persistent but silent infections in their natural host. Only exogenous species have been detected, and no diseases have been associated with spumavirus infections. No oncogenes have been detected in the genome. Often found in primary tissue cultures, especially on prolonged passage. In cell cultures syncytium formation is induced and the cells develop a foamy appearance. There are five recognized species: Bovine foamy virus, Chimpanzee foamy virus, Feline foamy virus, Simian foamy virus 1 and Simian foamy virus 3. Eleven serotypes have been isolated from monkeys of various species. No natural human infections are known, and the former human isolate is a simian virus. Viruses of simian, bovine and feline origin do not cross-react in neutralization tests. Virions, 100-140nm in diameter, have a distinctive morphology with an electron-lucent nucleoid core and envelope with prominent surface projections. The genome is 11kb in length (one monomer) and the LTR is 1150nt long (V3,800-R,200-U5,150). Maturation by budding. Inactivated by lipid solvents and pH 3. Replicate slowly in a wide range of dividing cells.

Loh PC (1993) In The Retroviridae, vol. 2, edited by JA Levy. New York: Plenum Press, p. 361 Rethwilm A (1995) Curr Top Microbiol Immunol 193.

Yu SF et al (1996) J Virol 70, 8255 Yu SF et al (1999) J Virol 73, 1565

Squirrel fibroma virus (SQFV) A species in the genus Leporipoxvirus, serologically related to Rabbit fibroma virus. Causes multiple fibromas in grey squirrels, Sciurus carolinensis, in N America. Produces fibromas in domestic rabbits but cannot be passaged in them. Synonym: fibroma virus of squirrels.

squirrel monkey herpesvirus

squirrel monkey herpesvirus Synonym for herpesvirus saimiri 2.

Squirrel monkey retrovirus (SMRV) A

species in the genus Betaretrovirus. An endogenous xenotropic virus of squirrel monkeys, Saimiri sciureus. Similar to Mason-Pfizer virus, although virions have a central electron-dense nucleoid while the Mason-Pfizer virus has a bipolar tubular nucleoid. Isolated from lung cells by co-cultivation with canine cells. Infectious for cells of human, mink, mouse, dog, bat, chimpanzee, rabbit and rhesus monkey, but not marmoset, owl monkey, baboon or howler monkey cells. Buds with an intact nucleoid through the cell membrane and has a reverse transcriptase with a magnesium cation preference. Viral RNA hybridized with the DNA from all the squirrel monkey tissues tested, but not with DNA from other New and Old World monkeys or apes. Not immunolog-ically related to oncoviruses of baboon, woolly monkey, rhesus monkey, cat, cattle, horses, rat, hamster or mouse.

Fine D and Schochetman G (1978) Cancer Res 38, 3123

Sommerfelt MA and Hunter E (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 1518

Squirrel parapoxvirus (SPPV) A species in the genus Parapoxvirus.

SR-11 virus (SR11V) A tentative species in the genus Hantavirus, isolated from rats, Rattus norvegicus, in Japan. Member of the Seoul virus antigenic group.

Src gene The oncogene of Rous sarcoma virus, inserted at the 3' end of the genome, which encodes a tyrosine kinase (pp60), anchored to the inner surface of the plasma membrane by a myristilated N-terminus. The v-SRC protein differs from the cellular protein (c-SRC) by several mutations, which result in an activated form of the enzyme in transformed cells, with increased amounts of phosphotyro-sine-containing proteins that presumably contribute to the transformed state. The crystal structure of Src has been obtained.

Brugge JS et al (1979) J Virol 29, 1196 Superti-Furga G and Gonfloni S (1997) BioEssays 19, 447

Sripur virus (SRIV) An unassigned vertebrate rhabdovirus, isolated from Sergentomyia sp in India in 1973. Not reported to cause disease in humans.

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