Saccharomyces cerevisiae virus L-A
Encyclopedia
Saccharomyces cerevisiae virus L-A is a double-stranded RNA
(dsRNA) virus of the yeast
Saccharomyces cerevisiae
. This virus
has a single 4.6 kb genomic segment that encodes its major coat protein, Gag (76 kDa) and a Gag-Pol fusion protein (180 kDa) formed by a -1 ribosomal frameshift. L-A can support the replication and encapsidation in separate viral particles of any of several satellite dsRNAs, called M dsRNAs, each of which encodes a secreted protein toxin (the killer toxin) and immunity to that toxin. L-A and M are transmitted from cell to cell by the cytoplasmic mixing that occurs in the process of mating. Neither is naturally released from the cell or enters cells by other mechanisms, but the high frequency of yeast mating in nature results in the wide distribution of these viruses in natural isolates. Moreover, the structural and functional similarities with dsRNA viruses of mammals has made it useful to consider these entities as viruses.
Double-stranded RNA viruses
Double-stranded RNA viruses are a diverse group of viruses that vary widely in host range , genome segment number , and virion organization...
(dsRNA) virus of the yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
. This virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
has a single 4.6 kb genomic segment that encodes its major coat protein, Gag (76 kDa) and a Gag-Pol fusion protein (180 kDa) formed by a -1 ribosomal frameshift. L-A can support the replication and encapsidation in separate viral particles of any of several satellite dsRNAs, called M dsRNAs, each of which encodes a secreted protein toxin (the killer toxin) and immunity to that toxin. L-A and M are transmitted from cell to cell by the cytoplasmic mixing that occurs in the process of mating. Neither is naturally released from the cell or enters cells by other mechanisms, but the high frequency of yeast mating in nature results in the wide distribution of these viruses in natural isolates. Moreover, the structural and functional similarities with dsRNA viruses of mammals has made it useful to consider these entities as viruses.
Viral replication cycle
Both the (+) and the (–) strands of L-A are synthesized within viral particles. Mature particles containing L-A dsRNA synthesize (+) strands (transcription) by a conservative mechanism, and extrude the new strand from the particles. These (+) strands serve as mRNA, to make coat proteins, and as the species encapsidated by those proteins to make new nucleoprotein particles. Encapsidated (+) strands are converted to dsRNA form (replication). The absence of both 5′ cap and 3′ poly(A) on the viral mRNA is the basis of complex interactions of virus and host in translation.Similarity of L-A to animal dsRNA viruses
Animal and plant dsRNA viruses have up to three capsid layers, with structures adapted to protect the virus in its extracellular travels, to facilitate uptake by specific target cells and to engineer the uncoating of the outer layers after uptake. The yeast L-A virus can dispense with much of this apparatus because of its strictly intracellular life cycle. However, both L-A and plant and animal dsRNA viruses synthesize both (+) and (–) viral RNA strands within particles. The core particles in the case of the animal viruses and the structures of these inner nucleoprotein particles are similar.See also
- Killer yeastsKiller yeastsA killer yeast is a yeast, such as Saccharomyces cerevisiae, which is able to secrete one of a number of toxic proteins which are lethal to receptive cells. The phenomenon was first observed by Louis Pasteur These yeast cells are immune to the toxic effects of the protein due to an intrinsic...
- Double-stranded RNA virusesDouble-stranded RNA virusesDouble-stranded RNA viruses are a diverse group of viruses that vary widely in host range , genome segment number , and virion organization...
- VirologyVirologyVirology is the study of viruses and virus-like agents: their structure, classification and evolution, their ways to infect and exploit cells for virus reproduction, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy...
- RNA virusRNA virusAn RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
- Virus classificationVirus classificationVirus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which...
- List of viruses