FIG. 3.

Disulfide-bonded gp70-Pr15E complexes are resistant to treatment with reducing agents in vivo. Amphotropic (A) and ecotropic (B) Mo-MLV env-expressing cells were labeled with l-[³⁵S]cysteine for 15 min and chased for 120 min. After 105 min of chase, the media were replaced with fresh media containing the indicated amounts of DTT. The chase was continued for 15 min, and then the cells were alkylated and solubilized. The Env protein was immunoprecipitated from the lysates with the polyclonal anti-MLV serum. The immunoprecipitates were analyzed under reducing and nonreducing conditions in SDS–12% polyacrylamide gels. (C) Samples of the immunoprecipitates of the amphotropic Env protein, derived from cells that had been treated with 0 or 5 mM DTT, were run in an SDS–8% polyacrylamide gel for better separation of the protein bands. The meaning of the designations gp85^red and gp85^ox is explained in Results. The samples were run under reducing (R) and nonreducing (NR) conditions.