Notes on Genus: Marafivirus

icosahedra

Type member: Maize rayado fino virus

Contents

Members of this Genus
General Description
Morphology
Electron Micrograph
Genome
Genus Genomic Organization
Genome Map
Type Member Genomic Organization
All Known Sequences
Curated Sequences

General Description

The genus Marafivirus (maize rayado fino virus group) is a small group of isometric viruses that are transmitted by leafhoppers and which multiply in their vectors. It is one of three genera in the family Tymoviridae, all of which have a similar particle morphology and which are related in phylogenetic analysis. Members differ from those of the other genera in having two coat proteins, and in addition those of the genus Tymovirus are beetle-transmitted while those of the genus Maculavirus have larger genomes, are phloem limited and have no known vectors.

Morphology

Virions isometric (icosahedral), not enveloped, 31 nm in diameter. Incomplete virus particles (empty capsids) are often present.

Virions composed of 25-30 % nucleic acid (in complete particles).

Genome

Monopartite, linear, single stranded, positive sense RNA 6000-7000 nucleotides long. There is no VPg at the 5'-terminus. Some members (but not the type member) have a polyA tail at the 3'-terminus.

Genus Genomic Organization

There is a large open reading frame producing a polyprotein of 221-227 kDa, which contains motifs characteristic for methyltransferase, helicase, RNA polymerase and papainlike protease activity. The coat protein is at the C terminus and occurs in plants as two sizes of about 21 and 25 kDa. It seems likely that the coat proteins are translated from a 3' coterminal subgenomic mRNA, but post-translational cleavage of the polyprotein is a possibility that has not been excluded. The type member also contains a second putative ORF that may encode a protein of 43 kDa with a distant relationship to Tymovirus movement proteins, but it is not known if this protein is expressed in vivo.

Type Member Genomic Organization

There is a large open reading frame producing a polyprotein of 224 kDa, which contains motifs characteristic for methyltransferase, helicase, RNA polymerase and papainlike protease activity. The coat protein is at the C terminus and occurs in plants as two sizes of 21.5 and 25 kDa. It seems likely that the coat proteins are translated from a 3' coterminal subgenomic mRNA, but post-translational cleavage of the polyprotein is a possibility that has not been excluded. There is a second putative ORF that may encode a protein of 43 kDa with a distant relationship to Tymovirus movement proteins, but it is not known if this protein is expressed in vivo.