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J Virol, August 1998, p. 6356-6361, Vol. 72, No. 8
Department of Pediatrics, Center for
Molecular Genetics, University of California, San Diego, La Jolla,
California 92093-0634
Received 9 January 1998/Accepted 22 April 1998
In the absence of envelope gene expression, retrovirus packaging
cell lines expressing Moloney murine leukemia virus (MLV) gag and pol genes produce large amounts of
noninfectious virus-like particles that contain reverse
transcriptase, processed Gag protein, and viral RNA
(gag-pol RNA particles). We demonstrate that these particles can be made infectious in an in vitro, cell-free system by
the addition of a surrogate envelope protein, the G spike
glycoprotein of vesicular stomatitis virus (VSV-G). The appearance of
infectivity is accompanied by physical association of the G
protein with the immature, noninfectious virus particles. Similarly,
exposure in vitro of wild-type VSV-G to a fusion-defective pseudotyped
virus containing a mutant VSV-G markedly increases the
infectivity of the virus to titers similar to those of conventional
VSV-G pseudotyped viruses. Furthermore, similar treatment of
an amphotropic murine leukemia virus significantly allows infection of
BHK cells not otherwise susceptible to infection with native
amphotropic virus. The partially cell-free virus maturation system
reported here should be useful for studies aimed at the preparation of
tissue-targeted retrovirus vectors and will also aid in
studies of nucleocapsid-envelope interactions during budding and of
virus assembly and virus-receptor interactions during virus uptake into
infected cells. It may also represent a potentially useful
step toward the eventual development of a completely cell-free
retrovirus assembly system.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
In Vitro Cell-Free Conversion of Noninfectious Moloney Retrovirus
Particles to an Infectious Form by the Addition of the Vesicular
Stomatitis Virus Surrogate Envelope G Protein


*
Corresponding author. Mailing address: Department of
Pediatrics, Center for Molecular Genetics, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0634. Phone: (619) 534-4268. Fax: (619) 534-1422. E-mail: tfriedmann{at}ucsd.edu.
Present address: First Department of Internal Medicine, Nagoya
University School of Medicine, Showa-ku, Nagoya 466, Japan.
Present address: Center for Gene Therapy, Chiron Technologies, San
Diego, CA 92121.
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