Saccharomyces cerevisiae virus L-A

Saccharomyces cerevisiae virus L-A, also called L-A helper virus, is a member of the Totiviridae family of viruses found primarily in Saccharomyces cerevisiae.^[3] Its discovery in the 1970s was the main starting point of research on yeast virology.^[4] It is a ~4.6 kb double-stranded RNA virus with no extracellular phase and so is inherited through vertical cytoplasmic transmission.^[4]

Saccharomyces cerevisiae virus L-A
ScV-L-A capsid protein structure and homodimer of the gag capsid protein
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Duplornaviricota
Class:	Chrymotiviricetes
Order:	Ghabrivirales
Family:	Totiviridae
Genus:	Totivirus
Species:	Saccharomyces cerevisiae virus L-A
Synonyms
Saccharomyces cerevisiae virus LA^[1] Saccharomyces cerevisiae virus ScV1^[2]

Replication cycle of L-A helper and M28 (K28) killer viruses in S. cerevisiae.

Additionally, in many strains of the yeast, it is found along with another virus called the M virus (or "M dsRNA", "Saccharomyces cerevisiae killer virus"), known to encode the killer toxin in many S. cerevisiae strains which confers the ability to kill neighboring sensitive cells that do not harbor the virus. It is indeed for this reason the virus is referred to as a helper virus, due to the M genome's dependence on it for its own survival and replication. (More recently, the M dsRNA is described as a satellite RNA.) A Yeast lineage with a M/killer virus is known as a "killer strain".^[5]

There are numerous apparently unrelated M dsRNAs that use L-A, their only similarity being their genome organization. The family of Totiviridae in general helps M-type dsRNAs in a wide variety of yeasts.^[5]

References

1. Francki, R.I.B.; Fauquet, C.M.; Knudson, D.L.; Brown, F., eds. (1991). Classification and nomenclature of viruses. Fifth report of the International Committee on Taxonomy of Viruses (PDF). Archives of Virology Supplementum 2.
2. "MINUTES OF THE SIXTH MEETING OF THE ICTV, SENDAI, 5th SEPTEMBER 1984" (PDF). International Committee on Taxonomy of Viruses (ICTV). 5 September 1984. Retrieved 10 February 2020.
3. Rodríguez-Cousiño, Nieves; Esteban, Rosa (2017-02-15). "Relationships and Evolution of Double-Stranded RNA Totiviruses of Yeasts Inferred from Analysis of L-A-2 and L-BC Variants in Wine Yeast Strain Populations". Applied and Environmental Microbiology. 83 (4). Bibcode:2017ApEnM..83E2991R. doi:10.1128/AEM.02991-16. PMC 5288835. PMID 27940540.
4. Schmitt, Manfred J.; Breinig, Frank (March 10, 2006). "Yeast viral killer toxins: lethality and self-protection". Nature Reviews Microbiology. 4 (3): 212–221. doi:10.1038/nrmicro1347. PMID 16489348. S2CID 24668951.
5. Ramírez, M; Velázquez, R; López-Piñeiro, A; Naranjo, B; Roig, F; Llorens, C (19 September 2017). "New Insights into the Genome Organization of Yeast Killer Viruses Based on "Atypical" Killer Strains Characterized by High-Throughput Sequencing". Toxins. 9 (9): 292. doi:10.3390/toxins9090292. PMC 5618225. PMID 28925975.