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Journal of Virology, December 1998, p. 9897-9905, Vol. 72, No. 12
Department of Biology, York University,
Toronto, Ontario, Canada M3J 1P3
Received 8 May 1998/Accepted 11 September 1998
Defective interfering (DI) RNAs of tomato bushy stunt virus (TBSV)
are small, subgenomic, helper-dependent replicons that are believed to
be generated primarily by aberrant events during replication of the
plus-sense RNA genome. Prototypical TBSV DI RNAs contain four
noncontiguous segments (regions I through IV) derived from the 5'
nontranslated region (NTR) (I), an internal section (II), and the
3'-terminal portion (III and IV) of the viral genome. We have studied
the formation of these molecules by using engineered precursor DI RNA
transcripts and report here the consistent accumulation of a novel
defective RNA species, designated RNA B. Northern blot, primer
extension, and sequence analyses indicated that, unlike prototypical DI
RNAs, RNA B lacks region I. In vitro transcripts corresponding to the
region II-III-IV structure of RNA B were amplified when coinoculated
with helper, indicating that the 5' NTR of the genome does not harbor
cis-acting replication elements essential for viral RNA
replication. Region I is, however, important for DI RNA fitness, since
molecules lacking it accumulated to significantly lower levels
(~10-fold reduction). Analysis of the minus-strand sequence of region
I led to the identification of an RNA undecamer sequence, arranged in
tandem, at its very 3' terminus. Additional variants of the undecamer
motif were also identified at internal positions in region I and in the
negative strands of regions II, III, and IV. Features of the undecamer motif, the consensus of which is (
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Formation and Amplification of a Novel Tombusvirus
Defective RNA Which Lacks the 5' Nontranslated Region of the
Viral Genome
)3'-CCCAAAGAGAG, are
consistent with a role as a cis-acting replication element.
It is proposed that the ability of RNA B to be amplified is due, in
part, to compensatory effects of a strategically positioned undecamer
motif in region II. Possible replicase-mediated mechanisms for the
generation of this novel viral RNA are also presented.
*
Corresponding author. Mailing address: Department of
Biology, York University, 4700 Keele St., Toronto, Ontario, Canada M3J 1P3. Phone: (416) 736-2100, ext. 40890 or 70352. Fax: (416) 736-5698. E-mail: kawhite{at}yorku.ca.
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