Notes on Genus: Picobirnavirus


Type member: Human picobirnavirus


General Description

This is currently the only genus in the family Picobirnaviridae. The name is derived from the Spanish pico (=small) with birna for bipartite RNA.


Virions isometric (icosahedral), not enveloped, 35-40 nm in diameter.


Bipartite double-stranded RNA totalling 4-4.5 kb.

Genus Genomic Organization

The larger segment (A) has two or three ORFs, the last one of which is the coat protein. The single ORF of segment B encodes an RNA-dependent RNA polymerase that has similarities to that of picornaviruses.

Type Member Genomic Organization

Segment A (2.5 kb) encodes:
  • ORF1: 25 kDa, non-structural protein of unknown function
  • ORF2: 62 kDa, Polyprotein that self-cleaves to yield the mature coat protein and another large peptide.
Segment B (1.7 kb) encodes a 61 kDa protein that is an RNA-dependent RNA polymerase.