Notes on Genus: Oleavirus
Type member: Olive latent virus 2
This is one of 6 genera in the family Bromoviridae
and derives its name from the scientific name of the host of the type member (olive = Olea europaea
). In common with other members of the family, it has a tripartite genome and an encapsidated subgenomic RNA. It differs from the other genera in having bacilliform particles of several sizes and a much larger subgenomic RNA4 (>2 kb). It is also distinct in not being aphid-transmitted. At present it contains only one member, olive latent virus 2, and the description below is based on that virus.
Virions quasi-spherical, 26 nm in diameter, to bacilliform, 37, 43, 48 and 55 nm long and 18 nm wide. Symmetry icosahedral.
Virions composed of about 16 % nucleic acid (in all particle types).
Tripartite, linear, single-stranded, positive sense RNA, with segments of 3126 (RNA1), 2734 (RNA2) and 2438 (RNA3) nucleotides. RNA4, a subgenomic fragment of RNA3, 2078 nucleotides long, is also encapsidated but appears not to have messenger activity. The 3' terminus has neither a poly(A) tract nor a tRNA-like structure.
Genus Genomic Organization
There are four open reading frames (ORFs), one each on RNA1 and RNA2 and two on RNA3.
Type Member Genomic Organization
The four open reading frames result in the following proteins:
- Replication protein 1a (RNA1) containing methyltransferase and helicase domains, 103 kDa
- Polymerase 2a (RNA2), RNA-dependent RNA polymerase, 91 kDa
- Movement protein 3a (5' half of RNA3), 36 kDa, involved in cell-to-cell transport
- Coat protein 3b (3' half of RNA3 but expressed from the subgenomic RNA4), 20 kDa
RNA4 appears not to have messenger activity.