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J. Virol., 07 1997, 5148-5160, Vol 71, No. 7
F Fischer, CF Stegen, CA Koetzner and PS Masters
We have inserted heterologous genetic material into the nonessential gene 4
of the coronavirus mouse hepatitis virus (MHV) in order to test the
applicability of targeted RNA recombination for site-directed mutagenesis
of the MHV genome upstream of the nucleocapsid (N) gene and to develop
further genetic tools for site-directed mutagenesis of structural genes
other than N. Initially, a 19-nucleotide tag was inserted into the start of
gene 4a of MHV strain A59 with the N gene deletion mutant Alb4 as the
recipient virus. In further work, the entire gene for the green fluorescent
protein (GFP) was inserted in place of gene 4, creating the currently
largest known RNA virus. The expression of GFP was demonstrated by Western
blot analysis of infected cell lysates; however, the level of GFP
expression was not sufficient to allow detection of fluorescence of viral
plaques. Northern blot analysis of transcripts of GFP recombinants showed
the expected alteration of the pattern of the nested MHV subgenomic mRNAs.
Surprisingly, though, GFP recombinants also produced an RNA species that
was the same size as wild-type mRNA4. Analysis of the 5' end of this
species revealed that it was actually a collection of mRNAs originating
from 10 different genomic fusion sites, none possessing a canonical
intergenic sequence. The finding of these aberrant mRNAs suggests that
long-range RNA or the ribonucleoprotein structure of the MHV genome can
sometimes be the sole determinant of the site of initiation of
transcription.
Copyright © 1997, American Society for Microbiology
Analysis of a recombinant mouse hepatitis virus expressing a foreign gene reveals a novel aspect of coronavirus transcription
Department of Biomedical Sciences, State University of New York at Albany, 12237, USA.
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