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Journal of Virology, December 2001, p. 11328-11335, Vol. 75, No. 23
Aviron, Mountain View, California 94043
Received 20 July 2001/Accepted 13 September 2001
The M2-1 protein of human respiratory syncytial
virus (hRSV) promotes processive RNA synthesis and readthrough
at RSV gene junctions. It contains four highly conserved cysteines,
three of which are located in the Cys3-His1
motif at the N terminus of M2-1. Each of the four cysteines, at
positions 7, 15, 21, and 96, in the M2-1 protein of hRSV A2 strain was
individually replaced by glycines. When tested in an RSV
minigenome replicon system using
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.23.11328-11335.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Requirement of Cysteines and Length of the Human
Respiratory Syncytial Virus M2-1 Protein for Protein Function and
Virus Viability
-galactosidase as a reporter gene,
C7G, C15G, and C21G located in the Cys3-His1
motif showed a significant reduction in processive RNA synthesis
compared to wild-type (wt) M2-1. C96G, which lies outside the
Cys3-His1 motif, was fully functional in supporting processive RNA synthesis in vitro. Each of these cysteine substitutions was introduced into an infectious antigenomic cDNA clone
derived from hRSV A2 strain. Except for C96G, which resulted in a
viable virus, no viruses were recovered with mutations in the
Cys3-His1 motif. This indicates that the
Cys3-His1 motif is critical for M2-1 function
and for RSV replication. The functional requirement of the C terminus
of the M2-1 protein was examined by engineering premature stop codons
that caused truncations of 17, 46, or 67 amino acids from the C
terminus. A deletion of 46 or 67 amino acids abolished the synthesis of
full-length
-galactosidase mRNA and did not result in the recovery
of viable viruses. However, a deletion of 17 amino acids from the C
terminus of M2-1 reduced processive RNA synthesis in vitro and was well
tolerated by RSV. Relocation of the M2-1 termination codon upstream of
the M2-2 initiation codons did not significantly affect the expression of the M2-2 protein. Both rA2-Tr17 and rA2-C96G did not replicate as
efficiently as wt rA2 in HEp-2 cells and was restricted in replication
in the respiratory tracts of cotton rats.
*
Corresponding author. Mailing address: Aviron, 297 N. Bernardo Ave., Mountain View, CA 94043. Phone: (650) 919-6587. Fax: (650) 919-6610/6611. E-mail: hjin{at}aviron.com.
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