It has the smallest genome (8.9 kilobases) of any Mononegavirales species and is unique within that order in its ability to replicate within the host cell nucleus.
Borna virus was isolated from a diseased horse in the 1970s, but the virus particles were difficult to characterise. Nonetheless, the virus' genome has been characterised. It is a linear negative-sense single stranded RNA virus in the order of the mononegavirales. This order contains the family of lyssaviruses which includes the viruses responsible for rabies. A new family named the bornaviridae was created to hold this virus.
Several of the proteins encoded by the Borna virus genome have been characterised. The G glycoprotein is important for viral entry into the host cell.
The P40 nucleoprotein from BDV is multi-helical in structure and can be divided into two subdomains, each of which has an alpha-bundle topology. The nucleoprotein assembles into a planar homotetramer, with the RNA genome either wrapping around the outside of the tetramer or possibly fitting within the charged central channel of the tetramer .
Bornaviruses enter host cells by endocytosis. The viral genome and associated viral proteins is released into the cytoplasm following fusion of the viral envelope and the endosome membrane.Replication of the bornavirus occurs inside the nucleus. This is the only animal virus within the order Mononegavirales to do this. Many plant Rhabdoviruses replicate in the nucleus.
Bornaviruses have negative sense RNAgenomes The negative sense RNA is copied to make a positive sense RNA template. This template is then used to synthesise many copies of the negative sense RNA genome. This is like making copies of a mold, and then using these molds to make many more viruses.
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^Schwemmle, M. and Lipkin, W.I. (2004) Models and mechanisms of Bornavirus pathogenesis. Drug Discovery Today: Disease Mechanisms 1(2):211–216