Gene Ontology annotation through association of InterPro records with GO terms
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
Bunyamwera bunyavirus nonstructural protein NSs is a nonessential gene product that contributes to viral pathogenesis.
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NSs is dispensable for replication in cultured cells and in mice but contributes to virulence; BUNdelNSs forms smaller plaques, grows to about 1 log lower titres and kills mice more slowly after intracerebral inoculation.
"The generation of viruses lacking the NSs gene shows conclusively that the product is not essential for replication in either cultured cells or in mice, and thus NSs can be designated as an accessory protein."
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NSs is required for efficient shutoff of host-cell protein synthesis, though shutoff is reduced rather than abolished in its absence.
"At 48 h after infection, host cell protein synthesis was almost completely shut off in wt BUN-infected BHK cells."
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Loss of NSs converts BUNV from a non-inducer to a strong inducer of the interferon-beta promoter, with a thymidine kinase promoter control showing the effect is not merely reduced shutoff.
"This indicates that activation of the IFN-β promoter was specific and independent of the reduced ability of BUNdelNSs to shut off host cell protein synthesis."
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Cells infected with NSs-deleted virus accumulate about ten times more viral nucleocapsid protein than wild-type-infected cells.
"Quantification of this gel by using a PhosphorImager indicated that approximately 10 times more N protein was produced in cells infected with BUNdelNSs compared with wt BUN."
Inhibition of RNA polymerase II phosphorylation by a viral interferon antagonist.
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NSs targets the RNA polymerase II complex and prevents CTD serine 2 phosphorylation while serine 5 phosphorylation and promoter binding remain normal, implying a block between initiation and elongation.
"However, NSs prevented CTD phosphorylation at serine 2, suggesting a block in transition from initiation to elongation."
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RNA polymerase II still occupies the interferon-beta promoter in infected cells, so NSs acts after recruitment rather than by preventing initiation.
"Furthermore, RNAP II was able to bind to the IFN-beta gene promoter as revealed by chromatin immunoprecipitation analysis, indicating that the initiation of transcription was not disturbed by NSs."
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The CTD phosphorylation block is specific to mammalian cells and is not seen in insect cells, consistent with lytic infection of the vertebrate host and persistent infection of the vector.
"Surprisingly, no interference with CTD phosphorylation was observed in insect cells."
Bunyamwera bunyavirus nonstructural protein NSs counteracts the induction of alpha/beta interferon.
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Wild-type BUNV-infected cells contain neither interferon nor interferon mRNA whereas BUNdelNSs is a strong inducer; induction requires viral dsRNA and IRF-3 and correlates with NF-kappaB activation, placing the NSs block at transcriptional activation of the interferon genes rather than at sensing.
"IFN induction by BUNdelNSs correlated with activation of NF-kappaB and was dependent on virally produced double-stranded RNA and on the IFN transcription factor IRF-3."
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BUNdelNSs replicates to wild-type levels in cells and mice lacking a functional type I interferon system, showing that the growth defect is caused by the interferon it induces.
"Furthermore, both in cultured cells and in mice lacking a functional IFN-alpha/beta system, BUNdelNSs replicated to wild-type BUN levels, whereas in IFN-competent systems, wild-type BUN grew more efficiently."
Interaction of Bunyamwera Orthobunyavirus NSs protein with mediator protein MED8: a mechanism for inhibiting the interferon response.
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NSs binds the Mediator head-module subunit MED8 (yeast two-hybrid plus co-immunoprecipitation from mammalian cells), with the interaction domain mapped to NSs residues 81-93, a region containing the most C-terminally conserved orthobunyavirus NSs motif.
"The region encompassing amino acids 81 to 93 of NSs was shown to be essential for the interaction."
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A recombinant virus truncated in the MED8-interaction domain (BUNNSs-T83) behaves like the NSs deletion virus, failing to inhibit RNA polymerase II-driven reporter transcription, failing to suppress host protein expression and permitting interferon-beta mRNA synthesis.
"an RT-PCR signal specific for IFN-β mRNA was detected only in cells infected with BUNdelNSs or BUNNSsT83 virus, and no signal was detected in cells infected with wt BUNV or in mock-infected cells"
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RNA polymerase II is progressively destabilised in wild-type infection but remains stable in BUNdelNSs and BUNNSs-T83 infections, suggesting an NSs-dependent late degradation of the polymerase.
"RNA polymerase II levels decreased over time in wt BUNV-infected cells, while the protein appeared considerably more stable in BUNdelNSs2-infected cells."
The N-terminus of Bunyamwera orthobunyavirus NSs protein is essential for interferon antagonism.
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A virus expressing NSs lacking the N-terminal 21 residues retains the MED8-interaction domain yet still fails to block RNA polymerase II activity and is a potent interferon inducer, so MED8 binding is necessary but not sufficient for the transcription block.
"Strikingly, despite encoding an NSs protein that contains the Med8 interaction domain, mBUNNSs22 fails to block RNA polymerase II activity during infection."
Activation of PKR by Bunyamwera virus is independent of the viral interferon antagonist NSs.
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NSs does not inhibit the dsRNA-activated effectors PKR or RNase L; eIF-2alpha phosphorylation is similar in wild-type and NSs-deleted infection, so the NSs block is confined to interferon induction.
"NSs is different from other IFN antagonists, since it inhibits dsRNA-dependent IFN induction but has no effect on the dsRNA-activated PKR and RNase L systems."
Bunyamwera orthobunyavirus S-segment untranslated regions mediate poly(A) tail-independent translation.
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The PABP1-binding and nuclear-retention activity reported in this paper is attributed to the viral nucleocapsid protein N, not to NSs, although UniProt's P16494 FUNCTION block cites this paper for NSs involvement in PABP1 relocalisation.
"Furthermore, we demonstrate that the viral nucleocapsid protein binds to, and colocalizes with, PABP in the cytoplasm early in infection, followed by nuclear retention of PABP."
UniProtKB entry NSS_BUNYW (P16494), Bunyamwera virus non-structural protein NS-S