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J. Virol., Aug 1996, 5533-5540, Vol 70, No. 8
KH Kim and C Hemenway
A tobacco protoplast system was developed to analyze cis-acting sequences
required for potato virus X (PVX) replication. Protoplasts inoculated with
transcripts derived from a PVX cDNA clone or from clones containing
mutations in their 5' nontranslated regions (NTRs) were assayed for RNA
production by S1 nuclease protection assays. A time course of plus- and
minus-strand-RNA accumulation indicated that both minus- and plus-strand
PVX RNAs were detectable at 0.5 h postinoculation. Although minus-strand
RNAs accumulated more rapidly than plus-strand RNAs, maximum levels of
plus-strand RNAs were 40- to 80-fold higher. On the basis of these data,
time points were chosen for determination of RNA levels in protoplasts
inoculated with PVX clones containing deletions or an insertion in their 5'
NTRs. Deletions of more than 12 nucleotides from the 5' end, internal
deletions, and one insertion in the 5' NTR resulted in substantially
decreased levels of plus-strand-RNA production. In contrast, all modified
transcripts were functional for minus-strand-RNA synthesis, suggesting that
elements in the 5' NTR were not essential for minus-strand-RNA synthesis.
Further analysis of the 5' NTR deletion mutants indicated that all
mutations that decreased genomic plus-strand-RNA synthesis also decreased
synthesis of the two major subgenomic RNAs. These data indicate that
cis-acting elements from different regions of the 5' NTR are required for
plus-strand-RNA synthesis and that this process may be linked to synthesis
of subgenomic RNAs.
Copyright © 1996, American Society for Microbiology
The 5' nontranslated region of potato virus X RNA affects both genomic and subgenomic RNA synthesis
Department of Biochemistry, North Carolina State University, Raleigh 27695-7622, USA.
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