Effect of a single amino acid substitution in the V3 domain of the human immunodeficiency virus type 1: generation of revertant viruses to overcome defects in infectivity in specific cell types.

Proviral clones of human immunodeficiency virus type 1 which contained single amino acid changes in the envelope V3 region were constructed. PCR amplification of Sup-T1 T cells transfected with one such mutant, G312T, revealed low levels of virus that resulted in the generation of a revertant virus, in which an alanine replaced the threonine residue at amino acid 312. The revertant virus (rA312) was fully infectious in Sup-T1 cells but lacked the ability to infect AA5 cells. The presence of a second mutation in a subsequent revertant virus (rR306), in which arginine was substituted for serine at amino acid 306 within the V3 loop, restored the ability of the mutated virus to infect AA5 cells. Our data highlight the importance of the V3 loop in defining virus tropism for specific cell types in culture and further suggest that a degree of interplay exists among V3 loop residues that helps maintain or control its biological function of the virus.