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J. Virol., Dec 1997, 8973-8982, Vol 71, No. 12
A Bukreyev, SS Whitehead, BR Murphy and PL Collins
The small hydrophobic protein SH of human respiratory syncytial virus (RSV)
is a short transmembrane surface protein of unknown function. A full-length
cDNA of RSV strain A2 (subgroup A) antigenomic RNA was modified such that
the entire SH gene, including the transcription signals and the complete
mRNA-encoding sequence, was deleted and replaced by a synthetic intergenic
region. This reduced the length of the antigenome by 398 nucleotides and
ablated expression of 1 of the 10 RSV mRNAs. Recombinant virus containing
this engineered deletion was recovered, and the absence of the SH gene was
confirmed by reverse transcription in conjunction with PCR. Northern blot
analysis of intracellular RNAs and gel electrophoresis of labeled
intracellular proteins confirmed the lack of expression of the SH mRNA and
protein. The absence of the SH gene did not noticeably affect RNA
replication, but two effects on transcription were noted. First, synthesis
of the G, F, and M2 mRNAs was increased, presumably due to their being one
position closer to the promoter in the gene order. Second, transcription of
genes downstream of the engineered site exhibited a steeper gradient of
polarity. On monolayers of HEp-2 cells, the SH- minus virus produced
syncytia which were at least equivalent in size to those of the wild type
and produced plaques which were 70% larger. Furthermore, the SH-minus virus
grew somewhat better (up to 12.6-fold) than wild-type recombinant RSV in
certain cell lines. While the function of the SH protein remains to be
determined, it seems to be completely dispensable for growth in tissue
culture and fusion function. When inoculated intranasally into mice, the
SH-minus virus resembled the wild-type recombinant virus in its efficiency
of replication in the lungs, whereas it replicated 10-fold less efficiently
in the upper respiratory tract. In mice, the SH-minus and wild-type
recombinant viruses were similarly immunogenic and effective in inducing
resistance to virus challenge.
Copyright © 1997, American Society for Microbiology
Recombinant respiratory syncytial virus from which the entire SH gene has been deleted grows efficiently in cell culture and exhibits site- specific attenuation in the respiratory tract of the mouse
Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892-0720, USA.
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