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PubMedDate not supplied

Structure and nuclear localization signal of the SKI3 antiviral protein of Saccharomyces cerevisiae.

The yeast chromosomal genes SKI2, SKI3, SKI4, SKI6, SKI7 and SKI8 repress the replication of double-stranded RNA viruses, protecting the host from the otherwise lethal effects of the virus. We cloned and sequenced the SKI3 gene and found that it encodes a 163 kDa protein including a typical nuclear localization signal. Cell fractionation experiments show that the SKI3 gene product is indeed tightly associated with nuclei and that the putative nuclear localization sequence directs beta-galactosidase into the nucleus. However, fusion of a part of the SKI3 protein lacking this signal with beta-galactosidase also directs beta-galactosidase into the nucleus, suggesting the presence of a second nuclear localization signal. The SKI3 gene is only essential in the presence of an M double-stranded RNA virus.

Amino Acid Sequence↗
PubMed1990

Circular single-stranded RNA replicon in Saccharomyces cerevisiae.

Circular RNA replicons have been reported in plants and, in one case, in animal cells. We describe such an element in yeast. In certain yeast strains, a 20S RNA species appears on transfer of cells to acetate medium. This phenotype shows cytoplasmic (non-Mendelian) inheritance and the 20S RNA is associated with 23-kDa protein subunits as a 32S particle. We demonstrate that yeast 20S RNA is an independent replicon with no homology to host genomic, mitochondrial, or 2-microns plasmid DNA or to the L-A, L-BC, or M1 double-stranded RNA viruses of yeast. The circularity of the 20S RNA is shown by the apparent absence of 3' and 5' ends, by two-dimensional gel electrophoresis, and by electron microscopy. Replication of yeast 20S RNA proceeds through an RNA-RNA pathway, and a 10,000-fold amplification occurs on shift to acetate medium. The copy number of 20S RNA is also reduced severalfold by the SKI gene products, a host antiviral system that also lowers the copy numbers of yeast double-stranded RNA viruses. Yeast 20S RNA and the hepatitis delta virus show some similarities.

Genotype↗
PubMed1989

Synthesis and antiviral activity evaluation of 3'-fluoro-3'-deoxyribonucleosides: broad-spectrum antiviral activity of 3'-fluoro-3'-deoxyadenosine.

Five 3'-fluorinated ribonucleosides were prepared and evaluated for their inhibitory properties against different viruses. The synthesis of these compounds was achieved by treatment of 2',5'-di-O-tritylated nucleoside analogues possessing a xylo-configuration with diethylaminosulfur trifluoride, followed by deprotection. 3'-Fluoro-3'-deoxyadenosine was active against a broad range of viruses, encompassing both DNA viruses [pox (vaccinia)], single-stranded (+) RNA viruses [picorna (polio, Coxsackie B), toga (sindbis, Semliki Forest)] and double-stranded RNA viruses (reo). In its antiviral activity spectrum 3'-fluoro-3'-deoxyadenosine clearly differed from those adenosine analogues that are known as inhibitors of S-adenosylhomocysteine hydrolase. 3'-Fluoro-3'-deoxyadenosine also proved effective in vivo, in inhibiting tail lesion formation in mice inoculated intravenously with vaccinia virus.

Adenosylhomocysteinase↗
PubMed1981

Sequences at the 3' ends of yeast viral dsRNAs: proposed transcriptase and replicase initiation sites.

ScV is a double-stranded RNA virus of yeast consisting of two separately encapsidated dsRNAs (L and M). ScV-1 and ScV-2 are two dsRNA viruses present in two different yeast killer strains, K1 and K2. Our 3' end sequence analysis shows that the two sets of viral dsRNAs from ScV-1 and ScV-2 are very similar. Consensus sequences for transcriptase and replicase initiation are proposed. A stem and loop structure with a 3' terminal AUGC sequence, like that of several plant virus plus strand RNAs, is present at the putative replicase initiation site of one of the yeast viral RNA plus strands.

Base Sequence↗
PubMed2004

Mycocin production in Cryptococcus aquaticus.

Double-stranded RNA viruses of about 35 nm in diameter were isolated from a mycocin-secreting strain of Cryptococcus aquaticus. A derivative of this strain, lacking small dsRNA, was non-mycocinogenic and sensitive to its own toxin. The killing pattern of this mycocin was restricted to some species of the Cystofilobasidiales clade. Despite the differences in genome size of dsRNA viruses in mycocinogenic strains of Cryptococcus aquaticus, Cystofilobasidium sp. CBS 6569, Cystofilobasidium bisporidii, Cystofilobasidium infirmominiatum, Trichosporon pullulans and Xanthophyllomyces dendrorhous and killing patterns of their mycocins, the viral genomes showed homology in hybridisation experiments.

Cryptococcus↗
PubMed1995

Translation and M1 double-stranded RNA propagation: MAK18 = RPL41B and cycloheximide curing.

MAK18 is one of nearly 30 chromosomal genes of Saccharomyces cerevisiae necessary for propagation of the killer toxin-encoding M1 double-stranded RNA satellite of the L-A double-stranded RNA virus. We have cloned and sequenced MAK18 and find that it is identical to RPL41B, one of the two genes encoding large ribosomal subunit protein L41. The mak18-1 mutant is deficient in 60S subunits, which we suggest results in a preferential decrease in translation of viral poly(A)-deficient mRNA. We have reexamined the curing of M1 by low concentrations of cycloheximide (G. R. Fink and C. A. Styles, Proc. Natl. Acad. Sci. USA 69:2846-2849, 1972), which is known to act on ribosomal large subunit protein L29. We find that when M1 is supported by L-A proteins made from the poly(A)+ mRNA of a cDNA clone of L-A, cycloheximide does not decrease the M1 copy number, consistent with our hypothesis.

Cloning, Molecular↗
PubMed2006

Genetic reassortment of infectious bursal disease virus in nature.

Infectious bursal disease virus (IBDV), a double-stranded RNA virus, is a member of the Birnaviridae family. Four pathotypes of IBDV, attenuated, virulent, antigenic variant, and very virulent (vvIBDV), have been identified. We isolated and characterized the genomic reassortant IBDV strain ZJ2000 from severe field outbreaks in commercial flocks. Full-length genomic sequence analysis showed that ZJ2000 is a natural genetic reassortant virus with segments A and B derived from attenuated and very virulent strains of IBDV, respectively. ZJ2000 exhibited delayed replication kinetics as compared to attenuated strains. However, ZJ2000 was pathogenic to specific pathogen free (SPF) chickens and chicken embryos. Similar to a standard virulent IBDV strain, ZJ2000 caused 26.7% mortality, 100% morbidity, and severe bursal lesions at both gross and histopathological levels. Taken together, our data provide direct evidence for genetic reassortment of IBDV in nature, which may play an important role in the evolution, virulence, and host range of IBDV. Our data also suggest that VP2 is not the sole determinant of IBDV virulence, and that the RNA-dependent RNA polymerase protein, VP1, may play an important role in IBDV virulence. The discovery of reassortant viruses in nature suggests an additional risk of using live IBDV vaccines, which could act as genetic donors for genome reassortment.

Amino Acid Substitution↗
PubMed2006

Atlantic salmon ISG15: Expression and conjugation to cellular proteins in response to interferon, double-stranded RNA and virus infections.

ISG15 is one of the earliest and most predominant proteins to be induced in mammals following IFN-alpha/beta stimulation, which suggests that it has an important function in the interferon system. Similar to ubiquitin, ISG15 forms covalent conjugates with its target proteins, but free ISG15 is released from human lymphocytes and monocytes during IFN-alpha/beta stimulation. In this work we describe a 17.3 kDa ISG15 orthologue in Atlantic salmon (AsISG15) with characteristic features of ISG15 proteins including tandem ubiquitin-homology domains and a conserved carboxy-terminal conjugating motif (LRLRGG). Furthermore, Northern blot analysis revealed strong induction by polyinosinic polycytidylic acid (poly I:C) and by viral infections, while Western blot analysis using a specific antibody generated against AsISG15 confirmed induction mediated by recombinant Atlantic salmon IFN-alpha/beta and demonstrated conjugation of AsISG15 to cellular proteins. Interestingly, the pattern of AsISG15 modified target proteins differed during ISAV infection compared to direct IFN-alpha/beta stimulation. Immunoprecipitation experiments demonstrated extracellular, free AsISG15 in supernatants of leucocytes stimulated with poly I:C. Moreover, immunoprecipitation of an about 65 kDa ISAV protein from infected TO cells using anti-AsISG15 antiserum suggests that binding between the AsISG15 and the ISAV protein occurred. Taken together, the results suggest that AsISG15 has a role in the antiviral interferon response of Atlantic salmon.

Amino Acid Sequence↗
PubMedDate not supplied

Type I interferon gene expression: differential expression of IFN-A genes induced by viruses and double-stranded RNA.

The family of interferon regulatory transcription factors (IRF) participates in the virus-induced and dsRNA-stimulated transcriptional regulation of either type I IFN genes or a definite set of genes which can also be activated by IFN. In this review, we place emphasis on the role of IRF-3 that associates with the coactivators CBP and/or p300, together or not with IRF-7. These complexes bind to the PRDI, PRDI-like domains or to a number of ISRE sequences located in the promoter of these virus-inducible genes. We also discuss the involvement of the IRF-3-related complexes in the differential regulation of IFN-A genes.

Animals↗
PubMed1969

On the biosynthesis and structure of double-stranded RNA in vaccinia virus-infected cells.

The virus-specific, RNase-resistant RNA appearing in vaccinia virus-infected cells was directly shown to be an RNA duplex. After its melting and subsequent banding on Cs(2)SO(4) or incubation with DNase, the RNA could be reannealed and then hybridized with vaccinia virus DNA.The double-stranded virus-specific RNA appears to exist in the cell in the form of heterogeneous partially double-stranded RNA's sedimenting between 9 and 22S. The kinetics of the appearance of the double-stranded RNA in the cell show a dependence on the multiplicity of infection and suggest that the double-stranded RNA is a "late" product of viral intracellular biosynthesis. The synthesis of the double-stranded RNA is inhibited by actinomycin D.

Animals↗
PubMed1995

Cytopathology and release of an RNA virus from a strain of Trichomonas vaginalis.

A strain of Trichomonas vaginalis infected with a double-stranded RNA virus showed pronounced cytopathology in the form of giant syncytia generated by the recruitment of single cells. The giant cells ultimately lysed, releasing virus into the culture medium. In the infected cells, clusters of electron-dense particles resembling viral structures were found in the cytoplasm. In addition, distinctive inclusions composed of similar particles were present in the nuclei of some cells. Double-stranded viral RNA of 5.5 kbp was demonstrated in both cytoplasmic and nuclear fractions from these cells. Viral particles collected from the cell-free culture supernatant were of the same shape and size as the RNA virus isolated from a strain of T. vaginalis described previously (Wang & Wang, Journal of Biological Chemistry, 260: 3697-3702, 1985; Wang & Wang, Proceedings of the National Academy of Sciences of the U.S.A. 83: 7956-7960, 1986) which does not show this cytopathology.

Animals↗
PubMed1976

Permissiveness of mouse, monkey and hybrid cells to encephalomyocarditis (EMC) virus.

Encephalomyocarditis (EMC) virus replicates to high titre in permissive mouse kidney (MKS) cells but poorly in monkey kidney (CV1) cells. The permissiveness of monkey-mouse hybrid cells varies according to their chromosomal content. In monkey cells, the synthesis of both single-stranded and double-stranded virus RNA is restricted; in semi-permissive hybrid clones, the double-stranded RNA is synthesized normally, whereas the synthesis of the single-stranded RNA is inhibited. Thus, it seems that more than one restrictive event is responsible for the low permissiveness of monkey cells to EMC virus.

Animals↗
PubMed1990

A novel avian virus with trisegmented double-stranded RNA and further observations on previously described similar viruses with bisegmented genome.

The occurrence in chickens of small viruses with bisegmented double-stranded RNA (dsRNA) genome is confirmed and a new virus with similar properties but with three genome segments is described. Both differ from birnaviruses (Intervirology 25, 141-143, 1986) in having indistinct surface structure, smaller diameters (35 nm), and higher buoyant density (1.4 g/ml) in CsCl but are similar in these respects to viruses previously described in several mammals (Lancet 2, 103-104, 1988; J. Gen. Virol. 69, 2749-2754, 1988; Res. Vet. Sci, in press) under the tentative name of picobirnaviruses (PBV). Genome segment length estimations gave values of 2.6 and 1.9 kbp for the avian PBV and 2.9, 2.4 and 0.9 kbp for the trisegmented viruses. The source and pathogenic potential of these viruses remain to be established.

Animals↗
PubMed2003

Homotypic interactions of the infectious bursal disease virus proteins VP3, pVP2, VP4, and VP5: mapping of the interacting domains.

Infectious bursal disease virus (IBDV), a nonenveloped double-stranded RNA virus of chicken, encodes five proteins. Of these, the RNA-dependent RNA polymerase (VP1) is specified by the smaller genome segment, while the large segment directs synthesis of a nonstructural protein (VP5) and a structural protein precursor from which the capsid proteins pVP2 and VP3 as well as the viral protease VP4 are derived. Using the recently redefined processing sites of the precursor, we have reevaluated the homotypic interactions of the viral proteins using the yeast two-hybrid system. Except for VP1, which interacted weakly, all proteins appeared to self-associate strongly. Using a deletion mutagenesis approach, we subsequently mapped the interacting domains in these polypeptides, where possible confirming the observations made in the two-hybrid system by performing coimmunoprecipitation analyses of tagged protein constructs coexpressed in avian culture cells. The results revealed that pVP2 possesses multiple interaction domains, consistent with available structural information about this external capsid protein. VP3-VP3 interactions were mapped to the amino-terminal part of the polypeptide. Interestingly, this domain is distinct from two other interaction domains occurring in this internal capsid protein: while binding to VP1 has been mapped to the carboxy-terminal end of the protein, interaction with the genomic dsRNA segments has been suggested to occur just upstream thereof. No interaction sites could be assigned to the VP4 protein; any deletion applied abolished its self-association. Finally, one interaction domain was detected in the central, most hydrophobic region of VP5, supporting the idea that this virulence determinant may function as a membrane pore-forming protein in infected cells.

Animals↗
PubMed1999

RNA-dependent RNA polymerase activity associated with Eimeria necatrix virus particles containing either double-stranded or single-stranded RNA.

Single-stranded (ss) RNA containing and double-stranded (ds) RNA containing virus particles of Eimeria necatrix were isolated by centrifugation through a CsCl gradient. RNA from the gradient fractions was identified as single-stranded or double-stranded by probing northern blots with digoxigenin-labeled riboprobes. These probes were generated with SP6 and T7 RNA polymerases from a partial cDNA clone derived from 5.6-kb viral dsRNA of E. necatrix. RNA-dependent RNA polymerase (RDRP) activity was identified in these CsCl-purified virus particles. The polymerase products of the ssRNA particles consisted of dsRNA indicating replicase activity, whereas the polymerase products of the dsRNA particles consisted of ssRNA indicating transcriptase. activity. RNase treatment in high salt solution (0.3 M NaCl) of the pooled RDRP products revealed that the products consisted of both RNase-resistant dsRNA and RNase-sensitive ssRNA. These results show that both replicase and transcriptase activities were present in the purified virus. The digoxigenin-labeled products hybridized to both SP6 and T7 transcripts confirming the presence of both activities.

Animals↗
PubMed1972

Degradation of single- and double-stranded RNA by frog virus 3.

Purified preparations of frog virus 3 possess ribonuclease activities directed against single-and double-stranded RNA. Double-stranded RNAs isolated from purified reovirus type 3 and from HeLa cells infected with poliovirus and single-stranded poliovirus RNA from purified virus are readily degraded by incubation with frog virus 3. The mode of action of the nucleases is endonucleolytic. Under the assay conditions used for the viral enzyme, crude extracts of uninfected HeLa, L, and baby hamster kidney cells did not show enzyme activity against double-stranded RNA but exhibited activity against single-stranded RNA. The dependence of the viral nucleases on divalent cations for optimal activity and the inhibition of the cleavage of single-stranded RNA by 0.2 M NaCl suggests that the enzymes are either virus-coded or virus-induced.

Animals↗