Retained in vitro infectivity and cytopathogenicity of HIV-1 despite truncation of the C-terminal tail of the env gene product.

Five in-frame stop mutations in the HIV-1 env gene, which lead to the production of env gene products truncated within the cytoplasmic C-terminal tail, have been generated and their effects on membrane fusion capacity, glycoprotein incorporation into virus particles, infectivity, and cytopathogenicity were analyzed. The resulting truncated glycoproteins were processed normally, were transported to the cell surface, and were able to induce CD4-dependent membrane fusion. The membrane fusion capacity of one of the mutant glycoproteins with a truncation of 144 amino acids was increased to about double of that induced by wild-type glycoprotein. With a single exception, the truncated viral glycoproteins were incorporated into virus particles which were infectious and cytopathic for permissive MT-4 cells. The infection kinetics with the mutated viruses were, however, delayed to varying degrees in comparison to infection with wild-type virus. Nevertheless, in each case, PCR amplification and direct sequencing of viral DNA in the infected cultures confirmed the presence of the mutant and the absence of revertant DNA. The mutant virus encoding a viral glycoprotein with the longest truncation (144 amino acids), in which only 7 cytoplasmic C-terminal amino acids in gp41 remain, resulted in infection kinetics in MT-4 cells which were only marginally delayed in comparison to those induced by wild-type virus. This means that these C-terminal 144 amino acids of gp41 are not necessary for glycoprotein incorporation into virus particles nor do they significantly contribute to the infectivity nor the cytopathogenicity of HIV-1 in MT-4 cells.