Notes on Family: Betaflexiviridae
The family Flexiviridae
was originally created to contain plant-infecting viruses with:
- Flexuous filamentous virions 12-13 nm in diameter (giving the family its name)
- Monopartite, positive sense, ssRNA genomes with a 3'-polyA tail
- Translation of at least some ORFs from subgenomic mRNAs
- Up to 6 open reading frames ordered from 5' to 3':
- An alpha-like replication protein (150-250 kDa) containing conserved methyl transferase, helicase and RNA-dependent RNA polymerase (RdRp) motifs
- One or more movement proteins
- A single coat protein (CP) of 22-44 kDa
- A sixth ORF in some viruses, which may partially overlap the 3'-end of the CP gene and is thought to have nucleotide-binding properties.
Recently, the family has been divided
- to reflect the very different lineages of replication protein (potex-like and carla-like)
- to include some related viruses of fungi
- to support the inclusion of these viruses with members of the family Tymoviridae in the order Tymovirales.
The family Betaflexiviridae includes the plant viruses with a carla-like polymerase while those viruses with a smaller, potex-like, polymerase are now classified within the family Alphaflexiviridae.
Virions filamentous, not enveloped, 600-1000 nm or more long and 12-13 nm in diameter.
Monopartite, linear, polyadenylated ssRNA of 6.5-9.0 kb.
Genera in the Family
The genera are distinguished by the type of movement protein (triple gene block, TGB or a single protein of the '30K' superfamily), the number of ORFs and the sizes of the virion, the replication protein and the coat protein. Phylogenetic analysis also supports these distinctions: