Subunit interactions of vesicular stomatitis virus envelope glycoprotein stabilized by binding to viral matrix protein

The mechanism by which viral glycoproteins are incorporated into virus envelopes during budding from host membranes is a major question of virus assembly. Evidence is presented here that the envelope glycoprotein (G protein) of vesicular stomatitis virus binds to the viral matrix protein (M protein) in vitro with the specificity, reversibility, and affinity necessary to account for virus assembly in vivo. The assay for the interaction is based on the ability of M protein to stabilize the interaction of G protein subunits, which exist as trimers of identical subunits in the virus envelope. The interaction with M protein was shown by using G proteins labeled with fluorescent probes capable of detecting subunit dissociation and reassociation in vitro. The results show that the M protein isolated from virions either as purified soluble protein or as nucleocapsid-M protein complexes interacts with the G protein in vitro and that the reaction is reversible. The interaction between the G and M proteins was not serotype specific, but no interaction between the vesicular stomatitis virus M protein and the influenza virus hemagglutinin could be detected. These results support the conclusion that the interactions described here are the ones that govern assembly of G protein into virus envelopes in vivo.