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Journal of Virology, March 2001, p. 2337-2344, Vol. 75, No. 5
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.5.2337-2344.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Mutations in the Cytoplasmic Tail of Murine
Leukemia Virus Envelope Protein Suppress Fusion Inhibition by R
Peptide
Min
Li,
Chinglai
Yang, and
Richard W.
Compans*
Department of Microbiology and Immunology,
Emory University School of Medicine, Atlanta, Georgia 30322
Received Recieved 10 July 2000/Accepted 6 December 2000
During viral maturation, the cytoplasmic tail of the murine
leukemia virus (MuLV) envelope (Env) protein undergoes proteolytic cleavage by the viral protease to release the 16-amino-acid R peptide,
and this cleavage event activates the Env protein's fusion activity.
We introduced Gly and/or Ser residues at different positions upstream
of the R peptide in the cytoplasmic tail of the Friend MuLV Env protein
and investigated their effects on fusion activity. Expression in HeLa
T4 cells of a mutant Env protein with a single Gly
insertion after I619, five amino acids upstream from the R peptide,
induced syncytium formation with overlaid XC cells. Env proteins
containing single or double Gly-Ser insertions after F614, 10 amino
acids upstream from the R peptide, induced syncytium formation, and
mutant proteins with multiple Gly insertions induced various levels of
syncytium formation between HeLa T4 and XC cells. Immunoprecipitation and surface biotinylation assays showed that most
of the mutants had surface expression levels comparable to those of the
wild-type or R peptide-truncated Env proteins. Fluorescence dye
redistribution assays also showed no hemifusion in the Env proteins
which did not induce fusion. Our results indicate that insertion
mutations in the cytoplasmic tail of the MuLV Env protein can suppress
the inhibitory effect of the R peptide on membrane fusion and that
there are differences in the effects of insertions in two regions in
the cytoplasmic tail upstream of the R peptide.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Emory University School of Medicine,
Atlanta, GA 30322. Phone: (404) 727-5947. Fax: (404) 727-8250. E-mail: compans{at}microbio.emory.edu.
Journal of Virology, March 2001, p. 2337-2344, Vol. 75, No. 5
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.5.2337-2344.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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