Modified envelope protein expression and incorporation into retroviral vectors displaying TVTMs. (A and C) Comparative Env protein expression levels of WT CEE, WT CAE, TVTMs alone, WT CEE plus TVTMs, and WT CAE plus TVTMs in 293T cell lysates. (B and D) Comparative levels of virion incorporation of retroviral vectors bearing WT CEE, WT CAE, TVTMs alone, WT CEE plus TVTMs, and WT CAE plus TVTMs. Western analysis of gp70 and gag proteins was conducted using a rat monoclonal antibody, 83A25, against the C terminus of the gp70 Env and a polyclonal antibody against p30.