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Journal of Virology, April 1999, p. 2876-2885, Vol. 73, No. 4
Plant Pathology Department, Iowa State
University, Ames, Iowa 50011-1020
Received 12 October 1998/Accepted 4 January 1999
Barley yellow dwarf luteovirus (BYDV) generates three 3'-coterminal
subgenomic RNAs (sgRNAs) in infected cells. The promoter of sgRNA1 is a
putative hot spot for RNA recombination in luteovirus evolution. The
sgRNA1 transcription start site was mapped previously to either
nucleotide 2670 or nucleotide 2769 of BYDV genomic RNA (gRNA) in two
independent studies. Our data support the former initiation site. The
boundaries of the sgRNA1 promoter map between nucleotides 2595 and 2692 on genomic RNA. Computer prediction, phylogenetic comparison, and
structural probing revealed two stem-loops (SL1 and SL2) in the sgRNA1
promoter region on the negative strand. Promoter function was analyzed
by inoculating protoplasts with a full-length infectious clone of the
BYDV genome containing mutations in the sgRNA promoter. Because the
promoter is located in an essential coding region of the replicase
gene, we duplicated it in a nonessential part of the genome from which
a new sgRNA was expressed. Mutational analysis revealed that secondary
structure, but not the nucleotide sequence, was important at the base
of SL1. Regions with both RNA primary and secondary structural features
that contributed to transcription initiation were found at the top of
SL1. Primary sequence, but not the secondary structure, was required in
SL2, which includes the initiation site. Disruption of base pairing near the sgRNA1 start site increased the level of transcription three-
to fourfold. We propose that both primary and secondary structures of
the sgRNA1 promoter of BYDV play unique roles in sgRNA1 promoter
recognition and transcription initiation.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Primary and Secondary Structural Elements Required for
Synthesis of Barley Yellow Dwarf Virus Subgenomic RNA1
and
*
Corresponding author. Mailing address: Plant Pathology
Department, 351 Bessey Hall, Iowa State University, Ames, IA
50011-1020. Phone: (515) 294-2436. Fax: (515) 294-9420. E-mail:
wamiller{at}iastate.edu.
Paper no. J-18114 of the Iowa State University Agricultural and
Home Economics Experiment Station Project 3545.
Present address: Department of Microbiology, University of
Pennsylvania School of Medicine, Philadelphia, PA 19104-6076.
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