FIG. 1.

Pulse-chase analysis of env-expressing cells. BHK-21 cells infected with recSFV expressing the amphotropic (A through C) or ecotropic (D and E) Mo-MLV env gene were labeled for 15 min with l-[³⁵S]cysteine at 6 h postinoculation and chased for the indicated times. The Env protein was immunoprecipitated from the cell lysates and the media by use of the polyclonal anti-MLV serum (A, B, D, and E). The immunoprecipitates were run in SDS–12% polyacrylamide gels under reducing (A and D) and nonreducing (B and E) conditions. The part of the gel in panel A that contains the samples of media was exposed seven times longer than the part that contains the cell samples. The putative nontranslocated Env molecules (nontransl.) and disulfide-linked aggregates (aggr.) are indicated. A fraction of the lysate of amphotropic env-expressing cells that were chased for 180 min was used for immunoprecipitation with a monoclonal antibody against gp70 (C). The resulting precipitate was analyzed under reducing (R) and nonreducing (NR) conditions in an SDS–12% polyacrylamide gel.