Eukaryotic expression of Xq22.3 Env. (A) HeLa cells were transfected with three different Xq22.3 Env constructs as well as MSRV Env, and Syncytin-1. Xq22.3 Env rev and MSRV Env rev contain the respective sequences in reverse orientation and were used as controls. Forty-eight hours post transfection protein expression was studied by Western blot using the indicated primary antibodies. The arrow marks a nonspecific band of about 43 kDa seen in immunoblots incubated with mAbs 13H5A5 and 6A2B2. Another nonspecific band of about 70 kDa observed in immunoblots incubated with 6A2B2 is indicated by an arrowhead. (B) Prolonged exposure of the blot membrane to demonstrate expression of a protein in HeLa cells transfected with Xq22.3 Env FL but not in HeLa cells transfected with a control plasmid containing Xq22.3 Env in reverse orientation (Xq22.3 FL Env rev). The Xq22.3 Env lane, which was included for comparison revealed bands ranging between ~40 to ~53 kDa after overexposure.