Notes on Genus: Anulavirus
Type member: Pelargonium zonate spot virus
The genus Anulavirus
is one of 6 genera in the family Bromoviridae
. In common with other members of the family, it has a tripartite genome and an encapsidated subgenomic RNA from which the coat protein is expressed. It differs from the other genera in having quasi-spherical particles and an RNA3 (encoding the movement and coat proteins) that is slightly larger than RNA2. Phylogenetic analyses, the coat protein is distinct from all other genera in the family, while other genes cluster in different ways. At present it contains only one member, Pelargonium zonate spot virus, and the description below is based on that virus. The name is from the latin anular
=concentric, because of the concentric bands or ring symptoms shown in the major natural hosts (pelargonium, tomato).
Virions quasi-spherical, 25-35 nm in diameter with a poorly resolve surface structure.
Tripartite, linear, single-stranded, positive sense RNA, with segments of 3383 (RNA1), 2435 (RNA2) and 2659 (RNA3) nucleotides. 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, 108 kDa
- Polymerase 2a (RNA2), RNA-dependent RNA polymerase, 79 kDa
- Movement protein 3a (5' half of RNA3), 34 kDa, involved in cell-to-cell transport
- Coat protein 3b (3' half of RNA3 but expressed from the subgenomic RNA4), 23 kDa.