FIG. 4.

(A) Amino acid alignment of the VRA interloop domains of 4070A and Mo-MuLV envelope proteins. The conserved arginine residue is identified with an asterisk. Conserved residues are in capitals, and variable residues are in lowercase. (B) Incorporation of envelope proteins into retroviral vectors produced at 37°C. The upper blot was probed with anti-SU and anti-CA antibodies, and the lower blot was probed with anti-TM antibody. (C) Envelope proteins in the lysates of transfected 293T cells grown at 37°C, detected with anti-TM antibody. PR, precursor protein. Lanes No Env contain vectors produced without an env expression vector.