Nanoviridae

Nanovirus Babuvirus

The Nanoviridae are a family of viruses, including the following genera:
 * Genus Nanovirus; type species: Subterranean clover stunt virus
 * Genus Babuvirus; type species: Banana bunchy top virus

Virus structure and genome
Nanoviruses have a genome composed of a single strand of DNA which is arranged in a circular fashion. They have a multipartite genome, with between 6 and 11 circular ssDNAs, each of ~1kb. Their name is derived from the Greek word “nano” meaning dwarf, because of their small genome and also the stunting effect on infected plants.

Virions of this family have a simple composition: they have a capsid but no surrounding envelope. The capsid is round in shape, has a diameter of between 18-20 nm and displays icosahedral symmetry.

Replication
After infection of a host cell, the small DNA molecules that have become encapsidated with the genomic ssDNA act as primers. They bind to complementary regions and help in initiation of DNA synthesis by host polymerases. On completion of synthesis, there will be a double stranded intermediate that is transcribed unidirectionally. Most individual nanovirus particles only encode for a single protein.