Journal of Virology, July 2001, p. 5851-5859, Vol. 75, No. 13
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.13.5851-5859.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2363
Received 13 December 2000/Accepted 30 March 2001
The human immunodeficiency virus type 1 (HIV-1) accessory protein
Nef stimulates viral infectivity by facilitating an early event in the
HIV-1 life cycle. Although no structural or biochemical defects in
Nef-defective HIV-1 particles have been demonstrated, the Nef protein
is incorporated into HIV-1 particles. To localize the function of Nef
within the virus particle, we developed a novel technology involving
fusion of enveloped donor HIV-1 particles bearing core defects with
envelope-defective target virions bearing HIV-1 receptors. Although
neither virus alone was capable of infecting CD4+ target
cells, the incubation of donor and target virions prior to addition to
target cells resulted in infection. This effect, termed "virion
transcomplementation," required a functional Env protein on the donor
virus and CD4 and an appropriate coreceptor on target virions. To
provide evidence for intervirion fusion as the mechanism of
complementation, experiments were performed using dual-enveloped HIV-1
particles bearing both HIV-1 and ecotropic murine leukemia virus
(E-MLV) Env proteins as donor virions. Infection of CD4-negative target
cells bearing E-MLV receptors was prevented by HIV-1 entry inhibitors
when added before, but not after, incubation of donor and target
virions prior to the addition to cells. When we used Nef+
and Nef
donor and target virions, Nef enhanced infection
when present in donor virions. In contrast, no effect of Nef was
detected when present in the target virus. These results reveal a
potential mechanism for enhancing HIV-1 diversity in vivo through the
rescue of defective viral genomes and provide a novel genetic system for the functional analysis of virion-associated proteins in HIV-1 infection.
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