GaLV incompatibility with HIV-1 particles is modulated by residues 171N, 178K, and 179I. (A) Amino acid sequences of MLV and GaLV Env cytoplasmic tails. Chimeric mutations are indicated in boldface. (B) Relative percent infectivity with different chimeric Env proteins. (C) Comparison of amino acid sequences between MLV and GaLV in the region of residues 170 to 186. Variable amino acids are indicated in gray font. (D) Relative percent infectivity of Env point mutants. (E) Relative percent infectivity of MLV Env combination mutants. MLV Env proteins with K171N, Q178K, and A179I mutations (MLV NKI) and the V170I additional mutation (MLV INKI) are indicated. Infectivity is normalized to that of MLV Env. Averages and standard deviations from three independent experiments are shown. ****, P < 0.0001; ***, P < 0.001; **, P < 0.01; *, P < 0.05; ns, not significant (by unpaired and two-tailed Student's t test for each Env).