The envelope of rabies virus (a prototype member of the Rhabdovirus family) contains two kinds of major viral proteins, a transmembrane glycoprotein (G) and a matrix protein (M; formerly called M2), as well as some other host-derived minor components such as CD44 and CD99-related glycoprotein (VAP21) (11,(23)(24)(25). The M protein is a small-sized nonglycosylated internal protein (24-kDa), and is thought to be located underneath the lipid bilayer of the viral envelope where the protein is associated in some way with both the viral G protein and ribonucleoprotein (RNP) (26). Although the M protein is one of the major viral envelope components, detailed studies on the M protein have not been so frequently