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Journal of Virology, December 1998, p. 9621-9627, Vol. 72, No. 12
Laboratory of Molecular Microbiology,
National Institute of Allergy and Infectious Diseases, National
Institutes of Health, Bethesda, Maryland 20892-0460
Received 16 July 1998/Accepted 7 September 1998
We have identified mutations in the human immunodeficiency virus
type 1 (HIV-1) matrix protein (MA) which block infectivity of virions
pseudotyped with murine leukemia virus (MuLV) envelope (Env)
glycoproteins without affecting infectivity conferred by HIV-1 Env or
vesicular stomatitis virus G glycoproteins. This inhibition is very
potent and displays a strong transdominant effect; infectivity is
reduced more than 100-fold when wild-type and mutant molecular clones
are cotransfected at a 1:1 ratio. This phenomenon is observed with both
ecotropic and amphotropic MuLV Env. The MA mutations do not affect the
incorporation of MuLV Env into virions. We demonstrate that in HIV-1
virions pseudotyped with MuLV Env, the HIV-1 protease (PR) efficiently
catalyzes the cleavage of the p15(E) transmembrane (TM) protein to
p12(E). Immunoprecipitation analysis of pseudotyped virions reveals
that the mutant MA blocks this HIV-1 PR-mediated cleavage of MuLV TM.
Furthermore, the transdominant inhibition exerted by the mutant MA on
wild-type infectivity correlates with the relative level of p15(E)
cleavage. Consistent with the hypothesis that abrogation of infectivity
imposed by the mutant MA is due to inhibition of p15(E) cleavage,
mutant virions are significantly more infectious when pseudotyped with
a truncated p12(E) form of MuLV Env. These results indicate that HIV-1
Gag sequences can influence the viral PR-mediated processing of the MuLV TM Env protein p15(E). These findings have implications for the
development of HIV-1-based retroviral vectors pseudotyped with MuLV
Env, since p15(E) cleavage is essential for activating membrane fusion
and virus infectivity.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Cleavage of the Murine Leukemia Virus Transmembrane
Env Protein by Human Immunodeficiency Virus Type 1 Protease:
Transdominant Inhibition by Matrix Mutations
and
*
Corresponding author. Mailing address: Bldg. 4, Rm.
307, NIAID, NIH, Bethesda, MD 20892. Phone: (301) 402-3215. Fax: (301) 402-0226. E-mail: EFreed{at}nih.gov.
Present address: IGH, CNRS-UPR 1142, Montpellier, France.
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