Features of the Env leader protein and the N-terminal Gag domain of feline foamy virus important for virus morphogenesis.

Previous studies have shown that foamy virus (FV) particle budding, especially the involvement of the viral env glycoprotein is different from that of other (ortho) retroviruses: the N-terminal Env leader protein Elp is a constituent of released FV particles. A defined sequence in Elp required for particle budding binds to the MA domain of Gag. To extend these findings, we show that feline FV Elp is a membrane-anchored protein with the N-terminus located inside the particle. Thus, the internal/cytoplasmic domain of Elp has the correct topology for interacting with Gag during budding. In addition to Elp, an Elp-related protein of about 9 kDa was shown to be virion associated and is probably generated by cellular signal peptidases. Besides the function of Elp binding, the N-terminal domain of Gag was shown to be required for proper localization of feline FV Gag to the cytoplasm and the perinuclear/nuclear region.