FIG. 1.

Infection of NIH 3T3 cells by virions expressing various amounts of amphotropic Env in transient-transfection assays. Tel179.9 cells were transiently transfected with the PM377 amphotropic Env-expressing vector in the presence of various concentrations of DOX. (A) Env abundance assayed by immunoblotting. Equal amounts of cell extracts (a) and viral particles (b) were processed for immunoblotting analysis. Chemiluminescence detection was performed using a goat anti-MuLV Env antiserum. Only luminograms corresponding to short exposure times are presented in panels a and b. Longer exposures allowed visualization of Env expression at the highest DOX doses and thus quantification of signals (not shown). Both gp70 and its noncleaved precursor form, gp85, were detected in cellular extracts, and only gp70 was detected in experiments with viral particles. The blot presented in panel b was stripped and reprobed with anti-p30^Gag capsid monoclonal antibodies to verify that comparable amounts of viral proteins were analyzed in all tracks. The slight variations in p30^Gag protein abundance were taken into account for normalization of gp70 abundance. C-, nontransfected control cells. (B) FACS analysis of Env-expressing cells. Experiments were conducted using the 83A25 anti-Env rat monoclonal antibody.