| L-A helper virus | |
|---|---|
 | |
| 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: | Orthototiviridae |
| Genus: | Totivirus |
| Species: | Totivirus ichi |
| Synonyms | |
Saccharomyces cerevisiae virus L-A, also calledL-A helper virus, is a member of theTotivirus genus of viruses found primarily inSaccharomyces cerevisiae.[3] Its discovery in the 1970s was the main starting point of research on yeast virology.[4] It is a ~4.6kbdouble-stranded RNA virus with no extracellular phase and so is inherited throughvertical cytoplasmic transmission.[4]
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 manyS. 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 ahelper virus, due to the Mgenome's dependence on it for its own survival and replication. (More recently, the M dsRNA is described as asatellite 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 ofTotiviridae in general helps M-type dsRNAs in a wide variety of yeasts.[5]