Notes on Genus: Ophiovirus
Type member: Citrus psorosis virus
The genus Ophiovirus
is the only genus in the family Ophioviridae
and consists of viruses that have highly flexuous, fine filaments, rather resembling those in the genus Tenuivirus
. These sediment as two components that encapsidate at least 3 and probably 4 RNAs. RNA3 encodes the coat protein in the negative sense. The name is derived from the snake-like appearance of the virions (Greek ophis
Fine, flexuous filaments of two lengths, c.
10 nm in diam. and of 2 lengths (300-500 and 1500-2500 nm) representing 'top' and 'bottom' sedimentation components. These are collapsed double-stranded forms of nucleocapsid-like, highly flexuous open circles formed of filaments 3-4 nm in diam. Top-component filaments have contour lengths of 600-1000 nm, i.e. twice that reported for the corresponding collapsed form. Bottom-component filaments had contour lengths c.
4 times longer than those of top component filaments.
Linear, single-stranded RNA in 4 components. The largest is about 7.5-8.0 kb and the others are in the range, 1.4 to 1.8 kb. Most (or perhaps all) proteins are encoded in the negative sense.
Genus Genomic Organization
In the completely sequenced members of the genus:
- RNA1 (7.6-7.8 kb) encodes the large polymerase (262 kDa) and (potentially) a smaller protein of 22-25 kDa, both in the negative sense
- RNA2 (1.8 kb) encodes a 51-55 kDa protein of unknown function in the negative sense; there may also be a 10 kDa protein encoded in the virion sense near the 5'-terminus
- RNA3 (1.5 kb) encodes the coat protein (48-49 kDa) in the negative sense
- RNA4 (1.4 kb) encodes a 37-38 kDa protein of unknown function in the negative sense; a potential ORF of 10.5 kDa (also in the negative sense) at the 5'-end of the RNA may be expressed as a fusion with the larger protein by ribosomal frameshift
Type Member Genomic Organization
The virus has probably not been completely sequenced:
- RNA1 (8.2 kb) encodes the large polymerase (280 kDa) and (potentially) a smaller protein of 24 kDa, both in the negative sense
- RNA2 (1.6 kb) encodes a 54 kDa protein of unknown function in the negative sense
- RNA3 (1.5 kb) encodes the coat protein (49 kDa) in the negative sense
- RNA4 (if present) has not been sequenced