FIG. 2.

Expression of wild-type and mutant MuLV Env proteins. HeLa T₄ cells were infected with vTF7-3 at a multiplicity of infection of 10 for 1 h at 37°C and then transfected with plasmids containing genes encoding wild-type or insertion mutant Env proteins. At 12 h posttransfection, cells were labeled with 100 μCi of [³⁵S]methionine and [³⁵S]cysteine as described in Materials and Methods. After the labeling, cells were biotinylated and immunoprecipitated with antibodies against the F-MuLV Env protein plus protein A-agarose beads at 4°C overnight. The samples were prepared with reducing sample buffer and analyzed by SDS–10% PAGE. (A) Cell surface. (B) Cell lysate. (C) Culture medium. Lanes: 1, pGEM-3 vector control; 2, full-length MuLV Env (Menv); 3, MenvR-; 4, M614GS₁; 5, M614GS₂; 6, M614G₁; 7, M614G₂; 8, M614G₃; 9, M614G₄; 10, M614A₁; 11, M614A₂; 12, M614A₄; 13, M619G; 14, M619A; 15, M619GS₁; 16, M619GS₂; 17, M619GS₃; 18, M619A₁; 19, M619A₃. PRE, precursor protein.