Four years of monitoring for viral haemorrhagic septicaemia virus in marine waters around the United Kingdom.
(9/29)
Between 1995 and 1998, marine fish from around the coast of the UK were collected and samples analysed for viral haemorrhagic septicaemia virus (VHSV) using cell culture isolation methods. In 1997 and 1998 the samples were also analysed for VHSV by reverse transcription PCR (RT-PCR). A total of 1867 fish of 11 species were tested, but VHSV was isolated on only 1 occasion, from herring Clupea harengus, in 1996. However, despite VHSV not being isolated in 1997 and 1998, in both years samples of herring from the west and south coasts of England produced positive signals in the RT-PCR, and in 1997 cod from the east coast of England also produced positive signals in the RT-PCR. These results are believed to be true indications of the presence of VHSV nucleic acid in the fish. In 1997, birnaviruses from Serogroup B1 were isolated from herring (a previously unrecorded host for the virus) and cod Gadus morhua, and a birnavirus from Serogroup A2 was also isolated from cod. In 1998, an aquareovirus was isolated from haddock Melanogrammus aeglefinus, a previously unrecorded host for the virus. (+info)
Solar UV radiation does not inactivate marine birnavirus in coastal seawater.
(10/29)
We examined the inactivation kinetics of marine birnavirus (MABV) in a coastal sea, in seawater samples collected from 50 cm depth. MABV was added to both natural and autoclaved seawater at a concentration of 6 x 10(6.43) TCID50 (50% tissue culture infectious dose) ml(-1), put in dialysis tubes and incubated at the original depth. The inactivation of MABV by solar UV radiation was examined using light and dark tubes. The infectivity titer of MABV was measured by the TCID50 method using CHSE-214 cells. Virus infectivity in natural seawater decreased quickly and was below the detection limit by 270 min in both light and dark conditions; however, virus infectivity was maintained in the autoclaved seawater until 420 min. These results suggest that the loss of virus infectivity is not caused by sunlight UV radiation. (+info)
The birnavirus crystal structure reveals structural relationships among icosahedral viruses.
(11/29)
Double-stranded RNA virions are transcriptionally competent icosahedral particles that must translocate across a lipid bilayer to function within the cytoplasm of the target cell. Birnaviruses are unique among dsRNA viruses as they have a single T = 13 icosahedral shell, lacking the characteristic inner capsid observed in the others. We determined the crystal structures of the T = 1 subviral particle (260 angstroms in diameter) and of the T = 13 intact virus particle (700 angstroms in diameter) of an avian birnavirus to 3 angstroms and 7 angstroms resolution, respectively. Our results show that VP2, the only component of the virus icosahedral capsid, is homologous both to the capsid protein of positive-strand RNA viruses, like the T = 3 nodaviruses, and to the T = 13 capsid protein of members of the Reoviridae family of dsRNA viruses. Together, these results provide important insights into the multiple functions of the birnavirus capsid and reveal unexpected structural relationships among icosahedral viruses. (+info)
Virus evolution: fitting lifestyles to a T.
(12/29)
The structure of a double-stranded RNA virus outer shell has revealed unexpected similarities with virions of positive-strand RNA viruses. These similarities intersect with emerging parallels in RNA replication to create intriguing evolutionary possibilities. (+info)
Structure of birnavirus-like particles determined by combined electron cryomicroscopy and X-ray crystallography.
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Birnaviruses possess a capsid with a single protein layer in contrast to most double-stranded RNA viruses infecting multicellular eukaryotes. Using freeze-drying and heavy metal shadowing, the capsids of two birnaviruses, infectious bursal disease virus (IBDV) and infectious pancreatic necrosis virus, as well as of an IBDV virus-like particle (VLP) are shown to follow the same T=13 laevo icosahedral geometry. The structure of the VLP was determined at a resolution of approximately 15 A (1.5 nm) by a combination of electron cryomicroscopy and a recently developed three-dimensional reconstruction method, where the scattering density is expressed in terms of symmetry-adapted functions. This reconstruction methodology is well adapted to the icosahedral symmetry of viruses and only requires a small number of images to analyse. The atomic model of the external capsid protein, VP2, recently determined by X-ray crystallography, fits well into the VLP reconstruction and occupies all the electron densities present in the map. Thus, similarly to the IBDV virion, only VP2 forms the icosahedral layer of the VLP. The other components of both VLP and IBDV particles that play a crucial role in the capsid assembly, VP1, VP3 and the peptides arising from the processing of pVP2, do not follow the icosahedral symmetry, allowing them to be involved in other processes such as RNA packaging. (+info)
Expression, purification and crystallization of a birnavirus-encoded protease, VP4, from blotched snakehead virus (BSNV).
(14/29)
Blotched snakehead virus (BSNV) is a member of the Birnaviridae family that requires a virally encoded protease known as VP4 in order to process its polyprotein into viral capsid protein precursors (pVP2 and VP3). VP4 belongs to a family of serine proteases that utilize a serine/lysine catalytic dyad mechanism. A mutant construct of VP4 with a short C-terminal truncation was overexpressed in Escherichia coli and purified to homogeneity for crystallization. Using the sitting-drop vapour-diffusion method at room temperature, protein crystals with two distinct morphologies were observed. Cubic crystals grown in PEG 2000 MME and magnesium acetate at pH 8.5 belong to space group I23, with unit-cell parameters a = b = c = 143.8 angstroms. Trigonal crystals grown in ammonium sulfate and glycerol at pH 8.5 belong to space group P321/P312, with unit-cell parameters a = b = 158.2, c = 126.4 angstroms. (+info)
The structure of a birnavirus polymerase reveals a distinct active site topology.
(15/29)
Single-subunit polymerases are universally encoded in both cellular organisms and viruses. Their three-dimensional structures have the shape of a right-hand with the active site located in the palm region, which has a topology similar to that of the RNA recognition motif (RRM) found in many RNA-binding proteins. Considering that polymerases have well conserved structures, it was surprising that the RNA-dependent RNA polymerases from birnaviruses, a group of dsRNA viruses, have their catalytic motifs arranged in a permuted order in sequence. Here we report the 2.5 A structure of a birnavirus VP1 in which the polymerase palm subdomain adopts a new active site topology that has not been previously observed in other polymerases. In addition, the polymerase motif C of VP1 has the sequence of -ADN-, a highly unusual feature for RNA-dependent polymerases. Through site-directed mutagenesis, we have shown that changing the VP1 motif C from -ADN- to -GDD- results in a mutant with an increased RNA synthesis activity. Our results indicate that the active site topology of VP1 may represent a newly developed branch in polymerase evolution, and that birnaviruses may have acquired the -ADN- mutation to control their growth rate. (+info)
Genome and polypeptides characterization of Tellina virus 1 reveals a fifth genetic cluster in the Birnaviridae family.
(16/29)
We characterized tellina virus 1 (TV-1), a birnavirus isolated from the marine bivalve mollusk Tellina tenuis. Genome sequence analysis established that TV-1 is representative of a viral cluster distant from other birnaviruses. The maturation process of the polyprotein encoded by the genomic segment A was delineated with the identification of the N-termini of the viral protease VP4 and the ribonucleoprotein VP3, and the characterization of peptides deriving from the processing of pVP2, the VP2 capsid protein precursor. One of these peptides was shown to possess a membrane-disrupting domain. Like the blotched snakehead virus, the polyprotein exhibits a non-structural polypeptide (named [X]) located between pVP2 and VP4. Mutagenesis analysis allowed the identification in VP4 of a catalytic Ser-Lys dyad that does not possess the common Gly-X-Ser signature of the serine hydrolases. The genomic segment B encodes the viral RNA-dependent RNA-polymerase VP1 with the unique sequence motif arrangement identified in other birnavirus VP1s. (+info)