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J. Virol., 02 1995, 720-727, Vol 69, No. 2
LA Ball
The larger segment (RNA 1) of the bipartite, positive-sense RNA genome of
the nodavirus flock house virus encodes the viral RNA-dependent RNA
polymerase. Two nonstructural viral proteins are made during the self-
directed replication of this RNA: protein A (110 kDa), the translation
product of RNA 1 itself, and protein B (11 kDa), the translation product of
a subgenomic RNA (RNA 3) that is produced from RNA 1 during replication. To
examine the roles of these proteins in RNA replication, specialized T7
transcription plasmids that contained wild-type or mutant copies of flock
house virus RNA 1 cDNA were constructed and used in cells infected with the
vaccinia virus-T7 RNA polymerase recombinant to make full-length
transcripts that directed their own replication. Sequences in the primary
transcripts that extended beyond the ends of the authentic RNA 1 sequence
inhibited self-directed RNA replication, but plasmids that were constructed
to minimize these terminal extensions produced primary transcripts that
replicated as abundantly as authentic RNA 1. Truncation or mutation of the
open reading frame for protein A eliminated self-directed replication,
although the mutant RNA 1 remained a competent template for replication by
wild-type protein A supplied in trans. These results showed that protein A
was essential for RNA replication and that the process was not inseparably
coupled to complete translation of the template. In contrast, protein B
could be eliminated without inhibiting replication by mutations that
disrupted the second of the two overlapping open reading frames on RNA 3.
Furthermore, a mutant of RNA 1 in which the first nucleotide of the RNA 3
region was changed from G to U replicated at levels as high as those of the
wild type without making either RNA 3 or protein B. However, diminishing
replication levels were observed during subsequent replicative passages of
RNA from both the mutants that could not make protein B. Roles for this
protein that could account for the subtle phenotype of these mutants are
discussed.
Copyright © 1995, American Society for Microbiology
Requirements for the self-directed replication of flock house virus RNA 1 [published erratum appears in J Virol 1995 Apr;69(4):2722]
Microbiology Department, University of Alabama at Birmingham 35294.
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