Notes on Genus: Alphacarmotetravirus

icosahedra

Type member: Providence virus

Contents

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

General Description

This is the first, and currently the only, genus in the family Carmotetraviridae and consists of viruses previously included in a single family of tetraviruses.This has now been split because of large differences in the types of RNA polymerase and other genome differences. In this family,there are unstructured genome terminal sequences, a unique readthrough signal controlling RdRp expression and a large third ORF overlapping with the replication protein that has a distant relationship to the 'carmo' supergroup of plant viruses.

Morphology

Virions isometric (icosahedral), not enveloped, about 40 nm in diameter with T=4 icosahedral shell quasi-symmetry.

Genome

Monopartite positive sense single-stranded RNA of about 6.2 kb without a 3'-polyA tail.

Genus Genomic Organization

There are three major ORFs, one encoding a replication protein with a readthrough strategy to express the RNA polymerase and the other a coat protein precursor. The third, and largest, ORF is of unknown function.

Type Member Genomic Organization

There is a replication protein of 40 kDa with a 'leaky' stop codon which when supressed produces a larger protein of 104 kDa including the RNA polymerase. Downstream is a coat protein precursor of 81 kDa. Overlapping the large replication protein is a third ORF of 131 kDa with a distant relationship to the 'carmo' supergroup of plant viruses; its function is unknown.