|Group:||Group II (ssDNA)|
The Nanoviridae are a family of single stranded DNA viruses that infect plants.
Their name is derived from the Greek word 'nano (dwarf) because of their small genome and their stunting effect on infected plants.
Virus structure and genome
Virions of this family have a capsid and are non enveloped. The capsid is icosahedral with diameter of 18-20 nanometers.
The genome is composed of a multiple segments of single stranded circular DNA each ~1 kilobase in length. There between 6 and 11 circular segments depending on the genus. The segments each encode a single protein. There is a putative stem loop structure in the non-coding region of each segment which has a conserved 9-nucleotide sequence at its apex.
Each member has up to 4 segments encoding replication proteins of ~33 kiloDaltons (kDa). The other segments encode products of 10-20 kDa in size and include a coat protein of ~19 kDa and a protein with a retinoblastoma binding motif.
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.
- Genus Nanovirus; type species: Subterranean clover stunt virus
- Genus Babuvirus; type species: Banana bunchy top virus
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