ESCRT - Viral Budding

The release of viral particles, also known as viral budding, is a process by which free virions are released from within cells via the hijacking of host cell ESCRT machinery. Retroviruses, such as HIV-1 and human T-lymphotropic virus, as well as a number of enveloped viruses, including the Ebola virus, require ESCRT machinery to exit the host cell. The process is initiated by viral Gag proteins, the major structural proteins of retroviral coats, which interact with TSG101 of the ESCRT-I complex and the ALIX accessory protein. ESCRT-III subunits (only CHMP4 and CHMP2 being essential ) are recruited to the site of viral budding to constrict and sever the neck of the bud in a manner similar to that described for membrane abscission during cytokinesis. Vps4 then recycles the ESCRT-III components to the cytosol and the virus is released from the cell. Note that the mechanism described here utilizes metazoan proteins, as viral budding has been studied more extensively in metazoans.