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J. Virol., Feb 1997, 996-1003, Vol 71, No. 2
F Fischer, D Peng, ST Hingley, SR Weiss and PS Masters
The coronavirus mouse hepatitis virus (MHV) contains a large open reading
frame embedded entirely within the 5' half of its nucleocapsid (N) gene.
This internal gene (designated I) is in the +1 reading frame with respect
to the N gene, and it encodes a mostly hydrophobic 23-kDa polypeptide. We
have found that this protein is expressed in MHV- infected cells and that
it is a previously unrecognized structural protein of the virion. To
analyze the potential biological importance of the I gene, we disrupted its
expression by site-directed mutagenesis using targeted RNA recombination.
The start codon for I was replaced by a threonine codon, and a stop codon
was introduced at a short interval downstream. Both alterations created
silent changes in the N reading frame. In vitro translation studies showed
that these mutations completely abolished synthesis of I protein, and
immunological analysis of infected cell lysates confirmed this conclusion.
The MHV I mutant was viable and grew to high titer. However, the I mutant
had a reduced plaque size in comparison with its isogenic wild-type
counterpart, suggesting that expression of I confers some minor growth
advantage to the virus. The engineered mutations were stable during the
course of experimental infection in mice, and the I mutant showed no
significant differences from wild type in its ability to replicate in the
brains or livers of infected animals. These results demonstrate that I
protein is not essential for the replication of MHV either in tissue
culture or in its natural host.
Copyright © 1997, American Society for Microbiology
The internal open reading frame within the nucleocapsid gene of mouse hepatitis virus encodes a structural protein that is not essential for viral replication
Department of Biomedical Sciences, State University of New York at Albany, New York 12237, USA.
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