Effects of gag mutations on human immunodeficiency virus type 1 particle assembly, processing, and cyclophilin A incorporation.

A series of human immunodeficiency virus (HIV) mutants was constructed either by deletion or by linker insertion at various regions in the gag coding sequences. The ability of each mutant to assemble virus particles and to process them proteolytically, as well as incorporate cyclophilin A, was analyzed by Western immunoblot. This investigation indicated that most of the gag mutants were assembled and released at a level comparable to that of wild-type virus. In an assay involving a single cycle of infection, mutants containing significant levels of cyclophilin A showed less in trans interference effects on wild-type infectivity than did cyclophilin A-deficient mutants. Mutations in the N-terminal two-thirds of capsid protein severely disrupted cyclophilin A incorporation, but they affected virus processing only slightly to moderately. Virions released from cyclosporine-treated cells were processed, as well as virions made by the mock-treated cells. Also, protease inhibitor treatment had no detectable effect on the cyclophilin A incorporation. These results indicate that cyclophilin A incorporation is not required for virus particle processing and that virus processing does not affect cyclophilin A incorporation.