Budding of rabies virus particles in the absence of the spike glycoprotein.
Budding of enveloped viruses from cellular membranes is believed to de pend on the presence of transmembrane spike proteins interacting with cytoplasmic virus components. To address the mechanism of rhabdovirus budding, we generated rabies virus mutants deficient for the glycoprotein G or the G cytoplasmic tail. We found that spikeless rhabdovirus particles were released from cells infected with the G-deficient mutant, demonstrating that a viral surface protein is not required to drive the budding process. However, particle production is enhanced approximately 6-fold and 30-fold in the presence of tailless G or G, respectively. This reveals that G also possesses an intrinsic and independent exocytosis activity. We propose a model according to which efficient budding of rhabdoviruses is achieved by a concerted action of both core and spike proteins.