Evidence that the SKI antiviral system of Saccharomyces cerevisiae acts by blocking expression of viral mRNA.
The SKI2 gene is part of a host system that represses the copy number of the L-A double-stranded RNA (dsRNA) virus and its satellites M and X dsRNA, of the L-BC dsRNA virus, and of the single-stranded replicon 20S RNA. We show that SKI2 encodes a 145-kDa protein with motifs characteristic of helicases and nucleolar proteins and is essential only in cells carrying M dsRNA. Unexpectedly, Ski2p does not repress M1 dsRNA copy number when M1 is supported by aN L-A cDNA clone; nonetheless, it did lower the levels of M1 dsRNA-encoded toxin produced. Since toxin secretion from cDNA clones of M1 is unaffected by Ski2p, these data suggest that Ski2p acts by specifically blocking translation of viral mRNAs, perhaps recognizing the absence of cap or poly(A). In support of this idea, we find that Ski2p represses production of beta-galactosidase from RNA polymerase I [no cap and no poly(A)] transcripts but not from RNA polymerase II (capped) transcripts.
Widner
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WR
Section on Genetics of Simple Eukaryotes, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Wickner
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D000595:Amino Acid Sequence; D000998:Antiviral Agents; D001483:Base Sequence; D003001:Cloning, Molecular; D004271:DNA, Fungal; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012318:RNA Polymerase I / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D012367:RNA, Viral / Q000037:antagonists & inhibitors*; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D001616:beta-Galactosidase / Q000037:antagonists & inhibitors / Q000235:genetics
D000998:Antiviral Agents; D004271:DNA, Fungal; D005656:Fungal Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D012367:RNA, Viral; C081929:SKI2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; D012318:RNA Polymerase I; D001616:beta-Galactosidase