Notes on Genus: Macluravirus
flexuous filaments
Type member: Maclura mosaic virus
Contents
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 other genera in having insect transmission, and from the genus
Potyvirus in having shorter particles (650-660 nm in length) and apparently smaller genomes. Phylogenetic studies also support the recognition of a distinct genus. As in all the genera except the genus
Bymovirus, members have monopartite genomes. It is named after its type member,
maclura mosaic
virus.
Morphology
Virions filamentous, not enveloped, usually flexuous, 650-660 nm long and 12-15 nm in diameter. Symmetry helical with a pitch of 3.4 nm
Virions composed of 5 % nucleic acid and 95 % protein.
Genome
Monopartite, linear, single stranded, positive sense RNA. The only fully sequenced member has a genome of 8.2 kb. The 3' terminus has a poly(A) tract and the 5' terminus has a genome-linked protein (VPg).
Genus Genomic Organization
The only member of this genus for which there is a complete sequence is Chinese yam necrotic mosaic virus. As in other members of the family
Potyviridae, its genome is tranlsated into a single polyprotein, which is subsequently processed into functional products, with the coat protein at the C-terminus. However, it lacks the P1 protein that is present at the N-terminus of the polyprotein in other monopartite membes of the family.
Type Member Genomic Organization
There are only partial sequence data available for the type member. An isolate of Chinese yam necrotic mosaic virus has been fully sequenced and its genome is predicted to be translated into a single polyprotein of 297 kDa, from which an estimated nine functional products are produced by proteolytic processing:
| HC-Pro | | Helper component protease | | 29 kDa |
| P3 protein | | unknown function | | 35 kDa |
| '6K1' | | unknown function | | 7 kDa |
| CI | | Cylindrical inclusion putative helicase | | 74 kDa |
| '6K2' | | unknown function | | 9 kDa |
| VPg | | Genome-linked protein | | 21 kDa |
| NIa-Pro | | Nuclear Inclusion protease | | 24 kDa |
| NIb | | Nuclear Inclusion polymerase | | 65 kDa |
| CP | | coat protein | | 32 kDa |
An additional small ORF (PIPO) is generated by frameshifting within the second (P3) cistron.
