Victorivirus , a new genus of fungal viruses in the family Totiviridae
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Victorivirus, a new genus of fungal viruses in the family Totiviridae Said A. Ghabrial Æ Max L. Nibert
Received: 3 September 2008 / Accepted: 10 November 2008 / Published online: 24 December 2008 Ó Springer-Verlag 2008
Abstract The family Totiviridae comprises viruses with nonsegmented dsRNA genomes and isometric virions. A new genus, Victorivirus, has been approved for this family, named from the specific epithet of Helminthosporium victoriae, host of the type species, Helminthosporium victoriae virus 190S. Distinguishing characteristics of the 11 viruses so far assigned to this genus include infection of filamentous fungi, an apparently coupled termination–reinitiation mechanism for translating the RNA-dependent RNA polymerase as a separate product from the upstream capsid protein, and sequence-based phylogenetic grouping in a distinct clade from other family members.
Introduction The family Totiviridae encompasses a broad range of viruses characterized by isometric virions, *40 nm in diameter, that each contain a nonsegmented dsRNA genome coding in most cases for only a capsid protein (CP) and an RNA-dependent RNA polymerase (RdRp) [9]. Viruses of the 18 species assigned to the genera in this family as of spring 2008 by the International Committee on Taxonomy of Viruses (ICTV) persistently infect either
S. A. Ghabrial (&) Department of Plant Pathology, University of Kentucky, 1405 Veterans Drive, Lexington, KY 40546, USA e-mail: [email protected] M. L. Nibert Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
fungi or protozoa, although a similar virus causing disease in penaeid shrimp has been reported [25]. To date, only three genera have been formally recognized: Totivirus, Giardiavirus, and Leishmaniavirus. Viruses infecting yeast, smut, or filamentous fungi have been placed in the genus Totivirus, and ones infecting parasitic protozoa in the latter two genera. At least three different strategies for RdRp expression appear to be used among members of this family: (1) as a fusion with CP (CP/RdRp) consequent to ribosomal frameshifting, as in Saccharomyces cerevisiae viruses L-A (ScV-L-A) and L-BC and also among the viruses that infect parasitic protozoa [5, 6, 16, 18, 19]; (2) as a fusion with CP without the use of ribosomal frameshifting, as in Ustilago maydis virus H1, in which case the RdRp is putatively released from the fusion by proteolysis [17]; and—of prime relevance to this article—(3) as a separate protein consequent to an apparently coupled termination– reinitiation mechanism, as in Helminthosporium victoriae virus 190S (HvV190S) [14, 29] and proposed for other viruses that infect filamentous fungi [2, 9, 21, 23, 24, 26, 27, 32, 35]. Sequence-based analyses have shown that the HvV190S-like viruses moreover define a discrete phylogenetic clade [1, 2, 9, 21, 27]. The distinguishing characteristics of the HvV190S-like viruses led us to propose a new genus to encompass them. Establishment of this genus, named V
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