Notes on Genus: Hypovirus
Type member: Cryphonectria hypovirus 1
The genus Hypovirus
is the only genus in the family Hypoviridae
and is so named because the members cause decreased virulence (hypovirulence) in their phyopathogenic fungal host. The viruses do not produce virions. They were originally thought to have a dsRNA genome but it is now believed that the dsRNA found in vesicles in infected fungi is a replicative form of the RNA.
There are no virions, although vesicles 50-80nm in diameter containing dsRNA and polymerase activity can be found in infected fungi.
Monopartite, linear, single stranded RNA of about 10-13 kbp. The 3' terminus has a poly(A) tract and the 5' terminus is blocked in some members. Isolates often contain additional shorter length or satellite-like dsRNAs, the function of which are not known.
Genus Genomic Organization
The members that have been sequenced appear to have either one or two open reading frames. When present, the shorter ORF (ORFA) is 5'-proximal and is sometimes autocatalytically cleaved into two smaller products. The N-terminus of the larger (or only) ORFB is a protease that autocatalytically releases. The remaining polypeptide contains polymerase and helicase domains.
Type Member Genomic Organization
There are two ORFs, each of which undergoes further processing:
|ORFA (69 kDa) is autocatalytically cleaved into two products:|
|1. ||29 kDa||Protease|
|2. ||40 kDa||unknown function|
|ORFB (362 kDa) is autocatalytically cleaved into two products:|
|1. ||48 kDa||Protease|
|2. || 314 kDa||Replication protein: polyprotein containing polymerase and helicase domains |