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Nucleoprotein viral RNA and mRNA of Thogoto virus: a novel "cap-stealing" mechanism in tick-borne orthomyxoviruses?

ABSTRACT: Tick-borne Thogoto virus (THOV) represents the prototype virus of a new genus in the Orthomyxoviridae family. Its genome consists of six segments of negative-sense, single-stranded RNA. We have cloned and sequenced the fifth genomic segment, which codes for the viral nucleoprotein (NP). The deduced amino acid sequence shows 43% similarity to the NP of Dhori virus, a related tick-transmitted orthomyxovirus, and about 14% sequence similarity to those of the influenza viruses. To reveal the mechanism by which THOV initiates mRNA synthesis, we characterized the 5' ends of the NP mRNAs. Transcripts were recognized by a cap-specific monoclonal antibody, indicating that THOV mRNAs are capped. Surprisingly, no large heterogeneous extensions were found at the 5' end, as would have been expected if THOV were using a classical "cap-stealing" mechanism. We therefore propose that THOV is stealing only the cap structure with one or two additional nucleotides from cellular mRNAs to generate appropriate primers for initiation of viral mRNA transcription.

SUBMITTER: Weber F

PROVIDER: S-EPMC190924 | biostudies-other | 1996 Dec

REPOSITORIES: biostudies-other

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Nucleoprotein viral RNA and mRNA of Thogoto virus: a novel "cap-stealing" mechanism in tick-borne orthomyxoviruses?

Weber F F Haller O O Kochs G G

Journal of virology 19961201 12

Tick-borne Thogoto virus (THOV) represents the prototype virus of a new genus in the Orthomyxoviridae family. Its genome consists of six segments of negative-sense, single-stranded RNA. We have cloned and sequenced the fifth genomic segment, which codes for the viral nucleoprotein (NP). The deduced amino acid sequence shows 43% similarity to the NP of Dhori virus, a related tick-transmitted orthomyxovirus, and about 14% sequence similarity to those of the influenza viruses. To reveal the mechani ...[more]

PMID: 8970956

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Project description:Flavivirus is a positive-sense, single-stranded RNA viral genus, with members causing severe diseases in humans such as tick-borne encephalitis, yellow fever, and dengue fever. Flaviviruses are known to cause remodeling of intracellular membranes into small cavities, where replication of the viral RNA takes place. Nonstructural (NS) proteins are not part of the virus coat and are thought to participate in the formation of these viral replication compartments (RCs). Here, we used tick-borne encephalitis virus (TBEV) as a model for the flaviviruses and developed a stable human cell line in which the expression of NS proteins can be induced without viral RNA replication. The model system described provides a novel and benign tool for studies of the viral components under controlled expression levels. We show that the expression of six NS proteins is sufficient to induce infection-like dilation of the endoplasmic reticulum (ER) and the formation of RC-like membrane invaginations. The NS proteins form a membrane-associated complex in the ER, and electron tomography reveals that the dilated areas of the ER are closely associated with lipid droplets and mitochondria. We propose that the NS proteins drive the remodeling of ER membranes and that viral RNA, RNA replication, viral polymerase, and TBEV structural proteins are not required.IMPORTANCE TBEV infection causes a broad spectrum of symptoms, ranging from mild fever to severe encephalitis. Similar to other flaviviruses, TBEV exploits intracellular membranes to build RCs for viral replication. The viral NS proteins have been suggested to be involved in this process; however, the mechanism of RC formation and the roles of individual NS proteins remain unclear. To study how TBEV induces membrane remodeling, we developed an inducible stable cell system expressing the TBEV NS polyprotein in the absence of viral RNA replication. Using this system, we were able to reproduce RC-like vesicles that resembled the RCs formed in flavivirus-infected cells, in terms of morphology and size. This cell system is a robust tool to facilitate studies of flavivirus RC formation and is an ideal model for the screening of antiviral agents at a lower biosafety level.

Dataset Information

Nucleoprotein viral RNA and mRNA of Thogoto virus: a novel "cap-stealing" mechanism in tick-borne orthomyxoviruses?

Publications

Nucleoprotein viral RNA and mRNA of Thogoto virus: a novel "cap-stealing" mechanism in tick-borne orthomyxoviruses?

Similar Datasets

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