Notes on Genus: Mastrevirus

twinned icosahedra

Type member: Maize streak virus

General Description

This is one of 7 genera in the family Geminiviridae. It is also known as Geminivirus Subgroup I or the maize streak virus group. It differs from the genus Begomovirus in leafhopper transmission and in having a monopartite genome and from the genera Curtovirus and Topocuvirus because its members usually infect monocotyledonous plants and their genomes code for only 3 or 4 proteins (rather than 7 or 6, respectively).

Transmission is persistent (circulative, non-propagative) and usually by a single vector species.

Morphology

Virions are geminate (twinned) icosahedra, not enveloped, 38 nm long and 22 nm in diameter. The virion contains 110 coat protein subunits arranged as 22 pentameric capsomers.

Genome

Monopartite, closed circular, single stranded DNA, 2600-2800 nucleotides long.

Genus Genomic Organization

There are four ORFs, two each on the virus (+) and complementary (-) senses. The larger + sense ORF (V1) encodes the coat protein and the other is a cell-to-cell movement protein. The two complementary sense ORFs (C1 and C2) are exons (RepA and RepB) of a single replication gene expressed by transcript splicing. In most species, the smaller complementary sense ORF (C2) lacks a methionine start codon but C1 is also expressed independently.

Type Member Genomic Organization

Although up to seven potential open reading frames for products greater than 10 kDa have been identified, it seems that there are 3 proteins produced:

Two proteins are encoded in the + (virion) sense:
V2	11 kDa	Cell-to-cell movement protein
V1	27 kDa	Coat protein
Two proteins are encoded in the - (complementary) sense:
C1	31 kDa	Rep A replication-associated protein
C1:C2	41 kDa	Replication-associated (Rep) protein expressed from ORFs C1 and C2 by transcript splicing