FIG. 3.
Residues responsible for resistance of Friend MLV 57 (Friend) to Fv1b and Ref1. (A) Point mutations were introduced in the NB-tropic Friend MLV CA at positions 107, F(N107T), and 117, F(H117L), to match the N-tropic Akr-623 sequence and (B) at positions 92, F(D92E), and 124, F(A124S), to match the N-tropic F/NT1 sequence. F/NT1 corresponds to the Friend MLV57 CA into which the NT1 residues 33 to 133 have been swapped. All infections were performed as indicated in Fig. 1, and relative mean decreases in titers were calculated from at least three independent experiments as in Fig. 2.