FIG 1.

Generation of bicistronic vectors for Env library screening. (A) Schematic of the various vector backbones (left) and their corresponding viral titers (neomycin CFU [NCFU]/milliliter). The internal SV40 promoter was replaced with the M1 mutant variant (27) or the MLV SA sequence. Arrows mark the transcriptional start sites. Positions of the WPRE are indicated. ANOVA and a post hoc Dunnet test using pRVL-CP as a control were used to calculate significance. **, P < 0.05; *, P < 0.1. Error bars indicate the SEMs for at least three independent experiments. Ψ, MLV packaging signal. (B) Positions of the viral long terminal repeat (LTR), splice donor (SD), splice acceptor (SA), packaging signal (Ψ), env, and WPRE elements are indicated. The arrow marks the transcriptional start site. The position of the randomized 11 amino acids (X₁₁) within the VRA of the FeLV-A/C Env backbone is indicated.