Generation of infectious virus particles by transient co-expression of human immunodeficiency virus type 1 gag mutants.

We have demonstrated that COS7 cells transiently co-expressing myristylation-defective (Myr-) and protease-defective (PR-) human immunodeficiency virus (HIV) mutants can release infectious virions when co-transfected with an amphotropic murine leukaemia virus envelope protein expression plasmid (SV-A-MLV-env). In contrast, no infectious virions were detected when a PR-, noninfectious HIV gag mutant was co-expressed with the Myr- mutant, although the Myr- mutant could still process the immature core particles in trans. This result indicates that generation of functionally normal Gag proteins is required for virus infectivity in our complementation system. A mutant with a 56-amino-acid deletion in the N-terminal region of the capsid (CA) domain could still complement the PR- mutant to generate infectious virions, suggesting that the deletion mutant could provide a functional protease for processing in the PR- mutant. This result is consistent with the concept that mutations within the N-terminal region of the CA domain have no major effects on Gag-Pol incorporation into particles.