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J Virol, May 1998, p. 4320-4326, Vol. 72, No. 5
Department of Biological Sciences, University
of Warwick, Coventry CV4 7AL, United Kingdom
Received 14 November 1997/Accepted 10 February 1998
The 1,244-nucleotide genome of Semliki Forest virus (SFV) defective
interfering (DI) RNA 19 (DI-19) is coterminal with the infectious
genome and contains two major deletions. One deletion removes the end
of the nsP1 gene and the beginning of the nsP2 gene, and the other
removes the end of the nsP2 gene, the nsP3 and nsP4 genes, and all of
the structural protein genes (M. Thomson and N. J. Dimmock,
Virology 199:354-365, 1994). Like all DI SFV RNAs, DI-19 contains
three regions that are conserved. Region a comprises the 5' terminus
continuous with part of the nsP1 gene, region b comprises a central
part of the nsP2 gene, and region c comprises the 3' terminus and the
associated untranslated region. A deletion analysis of the
265-nucleotide b region (nucleotides 679 to 943, inclusive) was
undertaken to determine its role in genome replication and packaging
into DI virus particles. Deleted plasmids were constructed and
transcribed, and the resulting DI RNAs were transfected into
SFV-infected BHK cells. Putative progeny DI virus particles that had
been released into the tissue culture fluid were then serially passaged
in new monolayers together with added high-multiplicity SFV, and cells
and tissue culture fluids were tested for the presence of DI RNA by
reverse transcription-PCR. DI RNA that had all of the b region deleted
was replicated well in BHK-21 cells, as shown by the presence of large
amounts of negative-sense DI RNA and an increase in the amount of
positive-sense RNA in the cytoplasm, but was packaged very
inefficiently, as indicated by very low amounts of DI RNA in the tissue
culture fluid. The genome of a deletion mutant that retained the 3' 224 nucleotides of region b was packaged successfully, but one that retained only the 5' 41 nucleotides was not detected in the tissue culture fluid. These and other data suggest that nucleotides 720 to 777 of region b are of particular importance in the packaging process. This
finding agrees with data obtained with Ross River virus and contrasts
with the well-studied Sindbis alphavirus major packaging signal that is
located within the nsP1 gene.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Deletion Analysis of a Defective Interfering Semliki Forest Virus
RNA Genome Defines a Region in the nsP2 Sequence That Is
Required for Efficient Packaging of the Genome into Virus
Particles

and
*
Corresponding author. Mailing address: Department of
Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom. Phone: 44 1 203 523593. Fax: 44 1 203 523658. E-mail: nd{at}dna.bio.warwick.ac.uk.
Present address: Laboratory of Viral Diseases, NIAID, NIH,
Bethesda, MD 20892.
Present address: Liver Diseases Section, NIDDK, NIH, Bethesda, MD
20892.
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