Titration of ASLV-A Env pseudotyped NB-MLV on MDTF cells transduced with Tva800AGG or Tva800ATG. Cells were initially transduced at an MOI of approximately 1 i.u./cell with a delivery virus expressing Tva800 and YFP and challenged 3 days later with 5-600 μl ASLV-A pseudotyped NB-MLV expressing GFP (tester virus). Cells were analyzed by two-colour FACS after a further three days. Data are plotted as the percentage of delivery virus transduced cells (YFP positive) infected by tester virus (GFP positive). (A) Mock-transduced (open circles) and Tva800AGG (filled circles). (B) Tva800ATG-transduced. Shown are the combined results of two independent experiments for (A) and one experiment for (B).