FIG. 3.

MuLV and GaLV Env proteins. (A) Comparison of the sequences of the transmembrane (M) and cytoplasmic tail regions (T and R) of the GaLV SEATO and amphotropic 4070A MuLV Env proteins. Numbering for GaLV Env is from the start of the mature protein after removal of the signal peptide (60). The C terminus of the cytoplasmic tail (R) is cleaved from Env during virion maturation, leaving 16 amino acids in the tail of the mature Env protein (T). (B) Schematic of the truncated and substituted GaLV (open boxes) and MuLV (shaded boxes) Env proteins used in this study. Construct GM(618/9) is the GaLV Env with the substitutions K₆₁₈Q and I₆₁₉A, ∗∗.