DELETION ANALYSIS OF A DEFECTIVE INTERFERING SEMLIKI-FOREST-VIRUS RNAGENOME DEFINES A REGION IN THE NSP2 SEQUENCE THAT IS REQUIRED FOR EFFICIENT PACKAGING OF THE GENOME INTO VIRUS-PARTICLES
Cl. White et al., DELETION ANALYSIS OF A DEFECTIVE INTERFERING SEMLIKI-FOREST-VIRUS RNAGENOME DEFINES A REGION IN THE NSP2 SEQUENCE THAT IS REQUIRED FOR EFFICIENT PACKAGING OF THE GENOME INTO VIRUS-PARTICLES, Journal of virology, 72(5), 1998, pp. 4320-4326
The 1,244-nucleotide genome of Semliki Forest virus (SFV) defective in
terfering (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 t
he end of the nsP2 gene, the nsP3 and nsP4 genes, and all of the struc
tural protein genes (M. Thomson and N. J. Dimmock, Virology 199:354-36
5, 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 re
gion. 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 we
re constructed and transcribed, and the resulting DI RNAs were transfe
cted into SFV-infected BHK cells. Putative progeny DI virus particles
that had been released into the tissue culture fluid were then seriall
y 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 regi
on deleted was replicated well in BHK-21 cells, as shown by the presen
ce of large amounts of negative-sense DI RNA and an increase in the am
ount of positive-sense RNA in the cytoplasm, but was packaged very ine
fficiently, as indicated by very low amounts of DI RNA in the tissue c
ulture fluid. The genome of a deletion mutant that retained the 3' 224
nucleotides of region b was packaged successfully, but one that retai
ned only the 5' 41 nucleotides was not detected in the tissue culture
fluid. These and other data suggest that nucleotides 720 to 777 of reg
ion b are of particular importance in the packaging process. This find
ing agrees with data obtained with Ross River virus and contrasts with
the well-studied Sindbis alphavirus major packaging signal that is lo
cated within the nsP1 gene.