Establishment of a reverse genetics system for Schmallenberg virus, a newly emerged orthobunyavirus in Europe.

Schmallenberg virus (SBV) is a newly emerged orthobunyavirus that has caused widespread disease in cattle, sheep and goats in Europe. Like other orthobunyaviruses, SBV is characterized by a tripartite negative-sense RNA genome that encodes four structural and two non-structural proteins. This study showed that SBV has a wide in vitro host range, and that BHK-21 cells are a convenient host for both SBV propagation and assay by plaque titration.

The small genome segment of Bunyamwera orthobunyavirus harbours a single transcription-termination signal.

Transcription termination of the mRNA produced from the small (S) genome segment of Bunyamwera orthobunyavirus (BUNV) has previously been mapped to two cis-acting sequences located within the 5' UTR using a virus-free replication assay. The ability of these sequences to terminate transcription was attributed to the shared pentanucleotide motif 3'-UGUCG-5'. Taking advantage of our plasmid-based rescue system to generate recombinant viruses, we re-evaluated the importance of both pentanucleotide motifs as well as that of two other conserved sequences in transcription termination in vivo.

Interferon antagonist NSs of La Crosse virus triggers a DNA damage response-like degradation of transcribing RNA polymerase II.

La Crosse encephalitis virus (LACV) is a mosquito-borne member of the negative-strand RNA virus family Bunyaviridae. We have previously shown that the virulence factor NSs of LACV is an efficient inhibitor of the antiviral type I interferon system. A recombinant virus unable to express NSs (rLACVdelNSs) strongly induced interferon transcription, whereas the corresponding wt virus (rLACV) suppressed it.

Bunyamwera orthobunyavirus S-segment untranslated regions mediate poly(A) tail-independent translation.

The mRNAs of Bunyamwera virus (BUNV), the prototype of the Bunyaviridae family, possess a 5' cap structure but lack a 3' poly(A) tail, a common feature of eukaryotic mRNAs that greatly enhances translation efficiency. Viral mRNAs also contain untranslated regions (UTRs) that flank the coding sequence. Using model virus-like mRNAs that harbor the Renilla luciferase reporter gene, we found that the 3' UTR of the BUNV small-segment mRNA mediated efficient translation in the absence of a poly(A) tail.

Coronavirus non-structural protein 1 is a major pathogenicity factor: implications for the rational design of coronavirus vaccines.

Attenuated viral vaccines can be generated by targeting essential pathogenicity factors. We report here the rational design of an attenuated recombinant coronavirus vaccine based on a deletion in the coding sequence of the non-structural protein 1 (nsp1). In cell culture, nsp1 of mouse hepatitis virus (MHV), like its SARS-coronavirus homolog, strongly reduced cellular gene expression.

La Crosse bunyavirus nonstructural protein NSs serves to suppress the type I interferon system of mammalian hosts.

La Crosse virus (LACV) is a mosquito-transmitted member of the Bunyaviridae family that causes severe encephalitis in children. For the LACV nonstructural protein NSs, previous overexpression studies with mammalian cells had suggested two different functions, namely induction of apoptosis and inhibition of RNA interference (RNAi). Here, we demonstrate that mosquito cells persistently infected with LACV do not undergo apoptosis and mount a specific RNAi response.

Neurons produce type I interferon during viral encephalitis.

Type I interferons, also referred to as IFN-alpha/beta, form the first line of defense against viral infections. Major IFN-alpha/beta producers in the periphery are the plasmacytoid dendritic cells (pDCs). Constitutive expression of the IFN regulatory factor (IRF)-7 enables pDCs to rapidly synthesize large amounts of IFN-alpha/beta after viral infection.

Efficient cDNA-based rescue of La Crosse bunyaviruses expressing or lacking the nonstructural protein NSs.

La Crosse virus (LACV) belongs to the Bunyaviridae family and causes severe encephalitis in children. It has a negative-sense RNA genome which consists of the three segments L, M, and S. We successfully rescued LACV by transfection of just three plasmids, using a system which was previously established for Bunyamwera virus (Lowen et al.

Inhibition of RNA polymerase II phosphorylation by a viral interferon antagonist.

Many viruses subvert the cellular interferon (IFN) system with so-called IFN antagonists. Bunyamwera virus (BUNV) belongs to the family Bunyaviridae and is transmitted by arthropods. We have recently identified the nonstructural protein NSs of BUNV as a virulence factor that inhibits IFN-beta gene expression in the mammalian host.

Functional L polymerase of La Crosse virus allows in vivo reconstitution of recombinant nucleocapsids.

La Crosse virus (LACV), a member of the family Bunyaviridae, is the primary cause of paediatric encephalitis in the United States. In this study, a functional RNA polymerase (L) gene of LACV was cloned and a reverse genetics system established. A reporter minireplicon mimicking the viral genome was constructed by flanking the Renilla luciferase gene with the 3' and 5' noncoding regions of the genomic M segment.