Notes on Genus: Rymovirus

flexuous filaments
flexuous filaments

Type member: Ryegrass mosaic virus


General Description

This is one of the genera in the family Potyviridae. Like the other genera, it is characterised by its flexuous filamentous particles, inclusion bodies in infected plant cells and by having a polyprotein genome strategy. It differs from most of the others in having mite transmission (Abacarus hystrix) and from the genus Bymovirus in having a monopartite genome. Some viruses previously placed in this genus have now been moved to the new genus Tritimovirus on the basis of substantial differences in nucleotide homology and because they have a different vector species (Aceria tulipae). Recent sequence analyses have also shown that the species now remaining in the genus cluster with the genus Potyvirus and, unlike other genera in the family, do not form a distinct cluster of their own. There are therefore proposals to abolish the genus. It is named after its type member, ryegrass mosaic virus.


Virions filamentous, usually flexuous, not enveloped, 690-720 nm long and 12-15 nm in diameter. Symmetry helical with pitch of 3.4 nm.

Virions composed of 5 % nucleic acid and 95 % protein.


Monopartite, linear, single stranded, positive sense RNA, about 10,000 nucleotides long. The 3' terminus has a poly(A) tract and the 5' terminus has a genome-linked protein (VPg).

Genus Genomic Organization

Genome organisation appears to be uniform throughout this genus and resembles other monopartite members of the family Potyviridae. The genome is translated into a single polyprotein, which is subsequently processed into ten products, with the coat protein at the C-terminus. An additional small ORF (PIPO) is generated by frameshifting within the third (P3) cistron.

Type Member Genomic Organization

The genome is translated into a single polyprotein of 348 kDa, from which an estimated ten functional products are produced by proteolytic processing:
P1 protein     putative protease    29 kDa
HC-Pro putative helper component protease     52 kDa
P3 protein unknown function     40 kDa
6K1 unknown function    6 kDa
CI Cylindrical inclusion putative helicase     71 kDa
6K2 unknown function     6 kDa
VPg Genome-linked protein     22 kDa
NIa Nuclear Inclusion putative protease     27 kDa
NIb Nuclear Inclusion putative polymerase     50 kDa
CP coat protein     44 kDa
An additional small ORF (PIPO) is generated by frameshifting within the third (P3) cistron.