FIG. 5.

(A) RBD-dependent infection by Fr-MLV (env ΔRBD) as a function of the concentration of Fr-RBD or Fr-RBD (D86A). Human 293 mCAT1 cells were exposed to Fr-MLV (env ΔRBD) carrying lacZ in the presence of Fr-RBD (diamonds) or Fr-RBD (D86A) (squares) over a concentration range of 0 to 8,000 nM. Two days after exposure to virus, the cells were stained with 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside, and blue cells were counted. The experiments were performed in triplicate wells of a six-well plate. (B) Effect of an excess of Fr-RBD (D86A) on Fr-RBD-dependent infection by Fr-MLV (env ΔRBD). Human 293 mCAT1 cells were exposed to Fr-MLV (env ΔRBD) encoding lacZ alone or in the presence of either Fr-RBD (80 nM) or Fr-RBD (D86A) (200 nM) or both. Infection was assessed as described above. −, absent. The error bars represent ±1 standard error.