Notes on Genus: Cystovirus

enveloped spheres
enveloped spheres

Type member: Pseudomonas phage f6


General Description

This is the only genus in the family Cystoviridae. These are the only phage with dsRNA genomes.


Virions are spherical, about 85 nm in diameter, with an envelope and covered by spikes.


There are 3 linear segments of dsRNA of 6-7, 4-4.2 and 2.3-3 kbp.

Genus Genomic Organization

Each segment encodes four proteins. Proteins forming the polymerase complex are encoded on the largest segment, RNA-L. Absorption and fusion proteins that form the virion envelope are encoded on RNA-M, while proteins of the nucleocapsid core are encoded on the smallest segment, RNA-S.

Type Member Genomic Organization

The proteins encoded by the genome in their order in each segment are:
L774.9Packaging factor
274.9RNA polymerase
185.0Structural (framework)
617.3Membrane anchor protein
369.2Spike protein
137.6Membrane protein
S816.0Nucleocapsid surface protein
99.6Membrane assembly protein
1220.3Non-structural protein
524.1 or 23.3Endopeptidase