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Journal of Virology, October 1999, p. 8138-8144, Vol. 73, No. 10
Department of Microbiology and Immunology,
Emory University School of Medicine, Atlanta, Georgia 30322
Received 3 December 1998/Accepted 6 July 1999
In polarized epithelial cells, the assembly and release of human
immunodeficiency virus type 1 (HIV-1) occur at the basolateral side of
the plasma membrane, and the site of assembly is determined by the site
of expression of the Env protein. In order to investigate whether the
expression of the Env proteins exclusively in the endoplasmic reticulum
(ER) can alter the site of virus assembly, we coexpressed the simian
immunodeficiency virus (SIV) Gag protein and mutant SIV Env proteins
having an ER retrieval signal (KKXX motif). In cells expressing the
wild-type (wt) Env protein or coexpressing Env and Gag proteins, the
Env protein was processed into the surface (SU) and transmembrane (TM)
proteins. In contrast, in cells expressing the mutant Env proteins
alone or in combination with Gag, the Env proteins were retrieved to
the ER and were not proteolytically processed. Coexpression of the Gag
and ER-retained mutant Env proteins resulted in a transient decrease in
the release of the Gag protein into the medium, suggesting an
interaction between the Gag and ER-retrieved Env proteins. Using
saponin-permeabilized cells coexpressing Gag and Env proteins, we
obtained further evidence for Env-Gag interaction. A monoclonal
antibody specific to the SIV Gag protein was found to
coimmunoprecipitate both the Gag and Env proteins. The interaction was
specific, as coexpressed SIV Env proteins without the cytoplasmic tail
or a chimeric HIV-1 Env proteins with the CD4 cytoplasmic tail were not
coimmunoprecipitated by the Gag-specific antibody. Electron microscopic
analyses indicated that assembly of virus particles occurred only at
the surfaces of cells in which the Gag protein was coexpressed with
either the wt or ER-retrieved mutant Env protein. These data indicate that although the Env and Gag proteins interact intracellularly, the
site of assembly of SIV is not redirected to an intracellular organelle
by the retrieval of the Env protein to the ER.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Intracellular Interaction of Simian
Immunodeficiency Virus Gag and Env Proteins
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Emory University School of Medicine,
Atlanta, GA 30322. Phone: (404) 727-5847. Fax: (404) 727-8250. E-mail: compans{at}microbio.emory.edu.
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