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J Virol, April 1998, p. 3259-3267, Vol. 72, No. 4
Department of Biochemistry, University of
California, San Francisco, California 94143,1
and
Department of Cell Biology, University of Virginia Health
Sciences Center, Charlottesville, Virginia 229082
Received 8 July 1997/Accepted 23 December 1997
The transmembrane subunit (TM) of the avian leukosis and sarcoma
virus (ALSV) envelope glycoprotein (Env) contains a stretch of
conserved hydrophobic amino acids internal to its amino terminus (residues 21 to 42). By analogy with similar sequences in other viral
envelope glycoproteins, this region has been proposed to be a fusion
peptide. We investigated the role of this region by changing each of
three hydrophobic residues (Ile-21, Val-30, and Ile-39) to glutamatic
acid and lysine in the ALSV subgroup A Env. Like wild-type (wt) Env,
all six mutant Env proteins were proteolytically processed,
oligomerized, and expressed at the cell surface in a form that bound
Tva, the ALSV subgroup A receptor. Like wt Env, Ile21Glu, Ile21Lys,
Val30Glu, and Val30Lys changed conformation upon binding Tva, as
assayed by sensitivity to thermolysin. Ile39Glu and Ile39Lys were
cleaved by thermolysin in both the absence and presence of Tva.
Although incorporated into virus particles at approximately equal
levels, all mutant Envs were compromised in their ability to support
infection. The mutants at residues 21 and 30 showed levels of infection
2 to 3 orders of magnitude lower than that of wt Env. The mutants at
residue 39 were noninfectious. Furthermore, none of the mutants
displayed activity in a cell-cell fusion assay. Our results support the
contention that residues 21 to 42 of ALSV subgroup A Env constitute its
fusion peptide.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mutational Analysis of the Candidate Internal
Fusion Peptide of the Avian Leukosis and Sarcoma Virus Subgroup A
Envelope Glycoprotein
*
Corresponding author. Mailing address: Department of
Cell Biology, University of Virginia Health Sciences Center, Box 439, Charlottesville, VA 22908. Phone: (804) 924-2593. Fax: (804) 982-3912. E-mail: jw7g{at}virginia.edu.
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