The 5' ends of Thogoto virus (Orthomyxoviridae) mRNAs are homogeneous in both length and sequence

The tick-borne Thogoto virus (THOV) is the type species of a new genus in the family Orthomyxoviridae. Its genome comprises six segments of single-stranded, negative-sense RNA. Each segment possesses conserved regions of semicomplementary nucleotides at the 3 and 5 termini which strongly resemble those of influenza virus. An in vitro polymerase assay based on reconstituted THOV viral cores was developed, and activity was shown to rely on an interaction between the conserved 3-and 5-terminal sequences and to be primer dependent. Addition of globin mRNA primed transcription, catalyzing the addition of an extra nucleotide to the transcripts, corresponding to the 5-terminal m 7 G cap residue. Priming with various cap analogs suggested that THOV transcription is initiated preferentially with m 7 GpppAm and involves base pairing. This is the first experimental evidence of endonuclease activity in THOV as part of a unique cap-snatching mechanism.

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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In vitro polymerase activity of Thogoto virus: evidence for a unique cap-snatching mechanism in a tick-borne orthomyxovirus

Leahy¹,

Dessens²,

Nuttall³

1997

“…The heterogeneous sequence originating from cellular RNAs is then followed by a stretch of 12 to 16 conserved nucleotides in the different genome segments in the influenza viruses (7). The situation for the Thogoto virus is somewhat different: the mRNAs are found to be homogeneous in both length and sequence at their 5Ј ends (2,16,38). Using an in vitro polymerase assay, Leahy et al (16) demonstrated that the Thogoto virus preferentially initiates transcription with a cap-A structure, which can base pair with the 3Ј ultimate uracil of the vRNA.…”

Section: Sdd (mentioning

confidence: 99%

The Putative Polymerase Sequence of Infectious Salmon Anemia Virus Suggests a New Genus within the Orthomyxoviridae

Krossøy

Hordvik

Nilsen

et al. 1999

123

The infectious salmon anemia virus (ISAV) is an orthomyxovirus-like virus infecting teleosts. The disease caused by this virus has had major economic consequences for the Atlantic salmon farming industry in Norway, Canada, and Scotland. In this work, we report the cloning and sequencing of an ISAV-specific cDNA comprising 2,245 bp with an open reading frame coding for a predicted protein with a calculated molecular weight of 80.5 kDa. The putative protein sequence shows the core polymerase motifs characteristic of all viral RNA-dependent RNA polymerases. Comparison of the conserved motifs with the corresponding regions of other segmented negative-stranded RNA viruses shows a closer relationship with members of the Orthomyxoviridae than with viruses in other families. The putative ISAV polymerase protein (PB1) has a length of 708 amino acids, a charge of +22 at neutral pH, and a pI of 9.9, which are consistent with the properties of the PB1 proteins of other members of the family. Calculations of the distances between the different PB1 proteins indicate that the ISAV is distantly related to the other members of the family but more closely related to the influenza viruses than to the Thogoto viruses. Based on these and previously published results, we propose that the ISAV comprises a new, fifth genus in the Orthomyxoviridae.

“…THOV gene products are related to the influenza virus polymerase proteins PB1 (7), PA (13), and PB2 and nucleocapsid protein (14). Like that of influenza A virus (FLUA), each THOV segment possesses conserved regions of semicomplementary nucleotides at the 3Ј and 5Ј termini (7,13,14) and mRNA synthesis is primed by host-derived cap structures (1,8,14). Moreover, we recently reported that both the 3Ј and 5Ј sequences of virion RNA (vRNA) are required for vRNA promoter activity (8).…”

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confidence: 99%

Striking conformational similarities between the transcription promoters of Thogoto and influenza A viruses: evidence for intrastrand base pairing in the 5' promoter arm

Leahy¹,

Dessens²,

Nuttall³

1997

In the accompanying report, we describe an in vitro polymerase assay based on reconstituted Thogoto virus (THOV) cores which provided evidence of a double-stranded vRNA promoter consisting of both the 3 and 5 sequences of vRNA (M. B. Leahy, J. T. Dessens, and P. A. Nuttall, J. Virol. 71:8347-8351, 1997). This system was used to investigate further the THOV vRNA promoter structure by using short, synthetic vRNA promoters. The results obtained show that interstrand base pairing between residues 10 and 11 of the 3 promoter arm with residues 11 and 12 of the 5 promoter arm, respectively, is important for promoter activity. In addition, intrastrand base pairing between residues 2 and 3 with residues 9 and 8 of the 5 promoter arm, respectively, was shown to be involved in promoter activity, while no evidence of intrastrand base pairing between residues 2 and 9 of the 3 promoter arm was obtained. These observations are consistent with a hook-like structure in the 5 promoter arm of the THOV promoter. The THOV cores were able to transcribe an influenza A virus (FLUA) vRNA-like promoter, as well as hybrid THOV-FLUA promoters. Hence, the THOV and FLUA vRNA promoters appear to be both structurally and functionally similar.