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Prions and RNA viruses of Saccharomyces cerevisiae
1National Institute of Diabetes, Digestive and Kidney Disease, National Institute of Health, Bethesda, Maryland 20892-0830, USA.
Abstract:
Saccharomyces cerevisiae is host to the dsRNA viruses L-A (including its killer toxin-encoding satellite, M) and L-BC, the 20S and 23S ssRNA replicons, and the putative prions, [URE3] and [PSI]. review the genetic and biochemical evidence indicating that [URE3] and [PSI] are prion forms of Ure2p and Sup35p, respectively. Each has an N-terminal domain involved in propagation or generation of the prion state and a C-terminal domain responsible for the protein's normal function, nitrogen regulation, or translation termination, respectively. The L-A dsRNA virus expression, replication, and RNA packaging are reviewed. L-A uses a -1 ribosomal frameshift to produce a Gag-Pol fusion protein. The host SK12, SK13 and SK18 proteins block translation of nonpoly(A) mRNAs (such as viral mRNA). Mutants deficient in 60S ribosomal subunits replicate L-A poorly, but not if cells are also ski-. Interaction of 60S subunits with the 3' polyA is suggested. SKI1/XRN1 is a 5'--> 3' exoribonuclease that degrades uncapped mRNAs. The viral Gag protein decapitates cellular mRNAs apparently to decoy this enzyme from working on viral mRNA.
Insights
This review explores Saccharomyces cerevisiae
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Saccharomyces cerevisiae harbors various genetic elements including dsRNA viruses (L-A, M, L-BC), ssRNA replicons, and prions ([URE3], [PSI]).
- Prions [URE3] and [PSI] are identified as prion forms of Ure2p and Sup35p, respectively, with distinct functional domains.
- Viral elements like L-A dsRNA virus exhibit unique replication and expression strategies.
Purpose of the Study:
- To review genetic and biochemical evidence for prion formation in Ure2p and Sup35p.
- To elucidate the replication, expression, and RNA packaging mechanisms of the L-A dsRNA virus.
- To examine host-pathogen interactions involving viral components and cellular machinery.
Main Methods:
- Review of existing genetic and biochemical studies on prions and viral elements.
- Analysis of protein domain functions in prion propagation and normal cellular roles.
- Examination of viral strategies for gene expression and replication.
Main Results:
- Established [URE3] and [PSI] as prion forms of Ure2p and Sup35p, with N-terminal prion domains and C-terminal functional domains.
- L-A virus utilizes a -1 ribosomal frameshift for Gag-Pol fusion protein synthesis.
- Host factors (SK12, SK13, SK18, SKI1/XRN1) and ribosomal subunits play critical roles in viral mRNA translation and degradation.
Conclusions:
- Prion formation in yeast involves specific protein domains and cellular factors.
- The L-A virus employs sophisticated mechanisms for gene expression and evades host defenses.
- Host-pathogen interactions are crucial for understanding viral replication and propagation in Saccharomyces cerevisiae.