FIG. 3.

Immunoprecipitation of MuLV Env from wt, PR⁻, and MA mutant virions. HeLa cells were cotransfected with the env-negative HIV-1 molecular clone pNL4-3KFS (KFS), the HIV-1 MA mutant derivative pNL4-3KFS/20LK/73EK/82AT (KFS/20/73/82), or a derivative of pNL4-3KFS containing a mutation in the HIV-1 PR active site (PR⁻/KFS) and the ampho-MuLV Env expression vector pSVAMLVenv. Transfected cells were metabolically labeled with [³⁵S]Met, and virion-associated material was prepared and immunoprecipitated with anti-MuLV Env antiserum. Positions of the uncleaved p15(E) and cleaved p12(E) forms of the MuLV TM protein are indicated.