Viruses in the families Arteriviridae and Coronaviridae have enveloped virions which contain nonseg-mented, positive-stranded RNA, but the constituent genera differ markedly in genetic complexity and virion structure. Nevertheless, there are striking resemblances among the viruses in the organization and expression of their genomes, and sequence conservation among the polymerase polyproteins strongly suggests that they have a common ancestry. On this basis, the International Committee on Taxonomy of Viruses recently established a new order, Nidovirales, to contain the two families. Here, the common traits and distinguishing features of the Nidovirales are reviewed. r 1997 Academic Press KEY WORDS: arterivirus; coronavirus; torovirus; polyprotein processing; RNA recombination.

The molecular features of bovine viral diarrhoea virus (BVDV), a member of the Pestivirus genus currently classified in the Togaviridae, were examined for characteris-tics resembling those of the Flaviviridae family. Like flaviviruses, BVDV possesses a single-stranded RNA genome (approx. 4.3 x 10 6 Mr) deficient in a 3 ' poly(A) tract. This RNA has a single open reading frame spanning the length of the genome in the viral RNA sense (positive polarity), implying an expression strategy involving the processing of a precursor polyprotein. With the exception of several short but significant stretches of identical amino acids within two non-structural proteins, no extended regions of nucleotide or amino acid sequence homology between BVDV and representatives of three serological subgroups of mosquito-borne flaviviruses were noted. However, comparison of the organization of protein-coding domains along the genomes and the hydropathic profiles of amino acid sequences revealed pronounced similarities. It is proposed that Pestivirus, of which BVDV is the prototype member, should no longer be grouped in the Togaviridae family, but rather be considered a genus of non-arthropod-borne viruses within the Flaviviridae.

Abstract not found

Rio Bravo (RB) virus has been assigned to the family Flaviviridae on the basis of its antigenic relatedness to other members of this family. RB virus, unlike most members of the Flaviviridae, is believed not to have an arthropod vector. We examined biochemical and biophysical characteristics of RB virus to determine whether it should be assigned to the Flaviviridae and to compare it with arthropod-borne flaviviruses. Purified RB virus banded at a density of 1.18 g/ml in sucrose and had a sedimentation coefficient of about 200 S. Virions, negatively stained with ammonium molybdate, were spherical, had diameters of 42 nm, and appeared to be surrounded by envelopes bearing surface projections. The loss of infectivity after infectious virus was incubated with diethyl ether or sodium deoxycholate confirmed the presence of nvelopes. Partially purified RB virions contained single-stranded RNA, lacking 3 ' poly(A) tracts, that sedimented in a 15~o to 30~o sucrose gradient as one discrete band with a sedimentation coefficient of about 40 S. Most of the viral proteins in preparations of purified virus and in immunoprecipitates had similar electrophoretic mobilities and glycosylation patterns to known flavivirus proteins. Therefore, they were assigned the

Swine and ruminant pestiviruses require the same cellular factor to enter bovine cells

Swine and ruminant pestiviruses require the same cellular factor to enter bovine cells

The molecular features of bovine viral diarrhoea virus (BVDV), a member of the Pestivirus genus currently classified in the Togaviridae, were examined for characteristics resembling those of the Flaviviridae family. Like flaviviruses, BVDV possesses a single-stranded RNA genome (approx. 4.3 x 10 6 Mr) deficient in a 3 ' poly(A) tract. This RNA has a single open reading frame spanning the length of the genome in the viral RNA sense (positive polarity), implying an expression strategy involving the processing of a precursor polyprotein. With the exception of several short but significant stretches of identical amino acids within two non-structural proteins, no extended regions of nucleotide or amino acid sequence homology between BVDV and representatives of three serological subgroups of mosquito-borne flaviviruses were noted. However, comparison of the organization of protein-coding domains along the genomes and the hydropathic profiles of amino acid sequences revealed pronounced similarities. It is proposed that Pestivirus, of which BVDV is the prototype member, should no longer be grouped in the Togaviridae family, but rather be considered a genus of non-arthropod-borne viruses within the Flaviviridae.

iscom structure as an immune-enhancing moiety:

Peripheral blood mononuclear cells (PBL) from cattle known to be persistently viraemic with bovine viral diarrhoea virus (BVDV) following a foetal infection, were examined for the presence of viral antigens and cell-associated infectious virus. Using immunocytochemical techniques, physical separations of PBL subsets and virus isolation techniques (directly and by cocultivation) it was found that infection occurred in B and T lymphocytes, monocytes, and a group of cells designated null cells for lack of more specific classification. The latter three groups also supported viral replication, as infectious virus could be isolated from enriched cell populations. BVDV-like particles in cytoplasmic vesicles of PBL subsets were detected by electron microscopy.

proteins. particles containing rubella virus structural Expression and characterization of virus-like