Figure 2.

The late steps of retroviral particle formation: traffic, assembly and budding. The different stages of NC: immature NC in Gag and mature NC in the viral particle. Scheme of Gag-gRNA complexes trafficking within the cell and viral particle assembly and release. Upon export of the genomic RNA from the nucleus, the gRNA is translated into Gag and GagPol proteins that recruit the genome and traffic through the cytoplasm onto the assembly site et the plasma membrane; few Gag complexes with the viral genome anchor into the plasma membrane; Gag recognizes the PM phospholipids PI(4,5)P2 which triggers the anchoring of the myristate into the inner leaflet of the membrane, multimers of Gag thus accumulate at the assembly site which can be rafts or tetraspanins enriched microdomains and will serve as a plateform for particle budding; other cellular determinant can intervene to promote budding and particle release, such as the ESCRT machinery. Some preformed or formed virions can undergo endocytosis from the plasma membrane and create new virus-containing compartment (VVC) in the cell that could be released by exocytosis upon cellular signal. During release, the particle undergoes a maturation process due to the viral protease that cuts Gag and GagPol to specific sites which releases the structural proteins and enzymes in order to form the mature infectious particle, in which free NC proteins condensed on the genomic RNA inside the viral mature core. This phenomenon is a key determinant for particle morphogenesis and infectivity.