Notes on Family: Bunyaviridae
This family largely infects vertebrates and there are a small number of plant virus members, which form the genus Tospovirus
. These have large (100nm diameter) enveloped particles, circular in cross section and containing a central core of ssRNA.
Virions pleomorphic in shape and size, spheroidal and enveloped, 80-110 nm in diameter. 3 filamentous nucleocapsids per envelope, each 200-3000 nm long (depending on arrangement) and 2-2.5 nm in diameter. Symmetry helical.
Particles contain 1-2 % nucleic acid, over 50 % protein and 20-30 % lipid.
The genome consists of three negative or ambisense ssRNA segments, designated: L (large), M (medium) and S (small).
- The L segment encodes the viral RNA polymerase (negative sense)
- The M segment encodes two glycoproteins (negative sense) as a single gene product that is usually co-translationally cleaved. Tospoviruses also have a non-structural protein (NSm) encoded in the postive sense.
- The S segment encodes the coat protein (N) in the negative sense and some genera, including Tospovirus, have an additional non-structural protein (NSs) encoded in the postive sense.
The terminal nucleotide sequences of each segment are complementary, so that the RNAs form non-covalently closed circles.
Genera in the Family