FIG. 2.

Mutagenesis of FeLV-B VRA. (A) Sequences of BBB (FeLV-B) and AAA (A-MLV) VRAs. The VRA residues of FeLV-B were mutated to the corresponding A-MLV VRA residues by PCR mutagenesis. Unchanged amino acids are indicated by dots, and divergent amino acids are underlined in the AAA VRA sequence. The cysteine residues that form the first disulfide-bonded loop in VRA and which are conserved in all mammalian type C retroviruses are in boldface. (B) Infection of MDTF cells expressing GGG (Pit1) or GGR receptor with lacZ pseudotype virus bearing mutant BBB (FeLV-B) envelopes. Topological diagrams of the chimeric receptors expressed by MDTF cells are shown above the histograms. Titers are mean values of three infection studies; error bars are indicated.