The nucleocapsid domain of FIV Gag plays a role in the recruitment of the ESCRT machinery to the site of viral budding

BACKGROUND: Several enveloped viruses exit from infected cells by hijacking the endosomal sorting complex required for transport (ESCRT) machinery. The main mechanisms evolved by the viruses to accomplish this task are represented by: i) the ubiquitination of structural viral proteins and ii) their direct interaction with ESCRT factors through short proline rich regions, known as late domains (L-domains). We have previously reported that the non-primate lentivirus feline immunodeficiency virus (FIV) is strictly dependent for its budding from a "PSAP"-type L-domain, mapping within the carboxy-terminal region of Gag. METHODS: In the present study, constructs expressing FIV Gag either wild type or characterized by different mutations within its carboxy-terminal region and/or specific nucleocapsid (NC) residues. These constructs were employed in order to investigate the role of AIP1/Alix, a specific component of the ESCRT machinery, and that of FIV Gag regions in viral budding. RESULTS: Here we demonstrate that the overexpression of AIP1/Alix rescues viral mutants lacking a functional PSAP motif, despite the absence of a canonical AIP1 binding domain within FIV Gag. Furthermore, we show that the AIP1 rescue ability is abolished by mutations in specific regions of the viral NC, thus demonstrating that NC is involved in functional interaction with Alix. CONCLUSIONS: Overall our results demonstrate that FIV Gag is able to recruit different ESCRT components by canonical (the PSAP L-domain) and non-canonical (NC) mechanisms, in order to maximize its chances of budding from infected cells.