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Journal of Virology, March 2000, p. 2949-2954, Vol. 74, No. 6
Departments of
Medicine1 and
Microbiology,2 University of Alabama at
Birmingham, Birmingham, Alabama 35294-2170
Received 25 June 1999/Accepted 8 December 1999
A putative cleavage site of the human foamy virus (HFV) envelope
glycoprotein (Env) was altered. Transient env expression revealed that the R572T mutant Env was normally expressed and modified
by asparagine-linked oligosaccharide chains. However, this
single-amino-acid substitution was sufficient to abolish all detectable
cleavage of the gp130 precursor polyprotein. Cell surface biotinylation
demonstrated that the uncleaved mutant gp130 was transported to the
plasma membrane. The uncleaved mutant protein was incapable of
syncytium formation. Glycoprotein-driven virion budding, a unique
aspect of HFV assembly, occurred despite the absence of Env cleavage.
We then substituted the R572T mutant env into a
replication-competent HFV molecular clone. Transfection of the mutant
viral DNA into BHK-21 cells followed by viral titration with the FAB
(foamy virus-activated
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of the R572T Point Mutant of a
Putative Cleavage Site in Human Foamy Virus Env
-galactosidase expression) assay revealed
that proteolysis of the HFV Env was essential for viral infectivity.
Wild-type HFV Env partially complemented the defective virus phenotype.
Taken together, these experimental results established the location of
the HFV Env proteolytic site; the effects of cleavage on Env transport,
processing, and function; and the importance of Env proteolysis for
virus maturation and infectivity.
*
Corresponding author. Mailing address: Division of
Infectious Diseases, 845 19th St. South, BBRB 220, University of
Alabama at Birmingham, Birmingham, AL 35294-2170. Phone: (205)
975-8982. Fax: (205) 975-6027. E-mail: mulligan{at}uab.edu.
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