A single amino acid substitution in HIV-1 reverse transcriptase significantly reduces virion release.

HIV-1 protease (PR) mediates the proteolytic processing of virus particles during or after virus budding. PR activation is thought to be triggered by appropriate Gag-Pol/Gag-Pol interaction; factors affecting this interaction either enhance or reduce PR-mediated cleavage efficiency, resulting in markedly reduced virion production or the release of inadequately processed virions. We previously showed that a Gag-Pol deletion mutation involving the reverse transcriptase tryptophan (Trp) repeat motif markedly impairs PR-mediated virus maturation and that an alanine substitution at W401 (W401A) or at both W401 and W402 (W401A/W402A) partially or almost completely negates the enhancement effect of efavirenz (a nonnucleoside reverse transcriptase inhibitor) on PR-mediated virus processing efficiency. These data suggest that the Trp repeat motif may contribute to the PR activation process. Here we demonstrate that due to enhanced Gag cleavage efficiency, W402 alanine or leucine substitution significantly reduces virus production. However, W402 replacement with phenylalanine does not significantly affect virus particle assembly or processing, but it does markedly impair viral infectivity in a single-cycle infection assay. Our results demonstrate that a single amino acid substitution at HIV-1 RT can radically affect virus assembly by enhancing Gag cleavage efficiency, suggesting that in addition to contributing to RT biological function during the early stages of virus replication, the HIV-1 RT tryptophan repeat motif in a Gag-Pol context may play an important role in suppressing the premature activation of PR during late-stage virus replication.