Inhibition of human immunodeficiency virus type 1 particle formation by alterations of defined amino acids within the C terminus of the capsid protein.

In previous studies, we demonstrated that the substitution of amino acid triplets for alanines in the carboxy-terminal portion (amino acids 341-352: ATL EEM MTA CQC) of the capsid protein domain (p24) of human immunodeficiency virus type 1 (HIV-1) partly led to an inhibitory effect on the capacity to form virus-like particles (VLPs). In these experiments, the uncleaved Pr55gag precursor protein was expressed by recombinant vaccinia viruses. We have now investigated the effects of these mutations with respect to a replication-competent HI-provirus system. Substitution of amino acids 344-346 (EEM) for alanines, which was previously shown to lead to an inhibition of VLP formation, completely blocked assembly and release of HIV. A substantial reduction of HIV synthesis was also observed in the proviral system after exchange of amino acids 347-348 [MT(A)] which, in contrast, was formerly shown to result in an increased formation of VLPs. Western blot analysis of lysates of cells transfected with these mutated proviral constructs revealed an abnormal intracellular processing pattern of the Pr55gag precursor molecules. Further analyses suggest a structural aberration of these altered polyproteins as the basis for the observed block of virus formation.