Borna disease virus (BDV) is a neurotropic enveloped RNA virus that causes a non-cytolytic, persistent infection of the central nervous system in mammals. Members of this superfamily share the structure of BDV-M, the matrix protein (M-protein) of BDV which is essential for virus assembly and budding, mediating the interaction between the viral capsid, envelope, and glycoprotein spikes, in addition to being responsible for the structural stability and individual form of virus particles.

Structural studies on this protein have shown that heterologously expressed BDV-M co-purifies with and protects ssRNA oligonucleotides taken up from the expression host. This have revealed the ability of BDV-M to bind RNA and lipid membranes simultaneously, thus expanding the repertoire of M-protein functionalities PMID:19237566.