Notes on Genus: Nanovirus


Type member: Subterranean clover stunt virus


General Description

The genus Nanovirus (or Subterranean clover stunt virus group) is one of two genera in the family Nanoviridae, which consists of viruses with small (18-19 nm) isometric virions and a multipartite (6 to 8 or more segments) ssDNA genome, each segment of which is circular and about 1kb in size. The small size of the genome segments and the stunting effects often caused in plants explain the name (from the Greek nanos = small). It contains the legume-infecting members which probably have 8 (or more) monocistronic segments, while those with six segments and two unidirectionally transcribed ORFs on DNA1 have now been placed in the genus Babuvirus.


Virions isometric (icosahedral), not enveloped 18-19 nm in diameter.


Multipartite (8 or possibly more segments), closed circular single stranded DNA, each segment about 1kb in size. Additional DNA segments associated with some isolates and encoding replication-associated proteins are now regarded as alphasatellites.

Genus Genomic Organization

Segments are monocistronic. 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. Eight genomic segments (and some additional satellite-like rep DNAs) have been identified for Faba bean necrotic yellows virus. Fewer genomic segments have been identified for the other members but it is possible that more remain to be discovered.

Type Member Genomic Organization

Six genomic DNA components (and some additional satellite-like rep DNAs) have been identified each encoding a single protein:
putative product
DNA-M (1)1001 movement protein (12.7 kDa)
DNA-C (3)991 cell-cycle link (Clink) protein (19.0 kDa)
DNA-N (4)1002 nuclear shuttle protein (17.6 kDa)
DNA-S (5)998coat protein (18.7 kDa)
DNA-U1 (7)988non-structural protein U1 (16.9 kDa)
DNA-R (8)1005replication initiator protein M-Rep (33.2 kDa)