Notes on Genus: Alphacarmotetravirus

icosahedra
icosahedra

Type member: Providence virus

Contents

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.