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Journal of Virology, September 1999, p. 7421-7429, Vol. 73, No. 9
Department of Molecular Biology and
Microbiology, Tufts University School of Medicine, Boston,
Massachusetts 02111
Received 27 January 1999/Accepted 25 May 1999
The 3' untranslated region (3' UTR) between the 3' end of
env and the long terminal repeat is well conserved among
avian retroviruses and is essential for efficient replication. Deletion
of the dr1 element within the 3' UTR has been reported to have various
effects, including reduced levels of unspliced RNA in the cytoplasm,
decreased stability of unspliced RNA, decreased particle production,
and decreased genomic RNA packaging. To probe the role of specific sequences within dr1 in virus replication, site-directed mutagenesis was utilized to perturb parts of the predicted secondary structure of
dr1. Seven of thirteen mutations had no significant effect; the others
resulted in an approximately 10- to 20-fold reduction in replication.
These mutants were further characterized and found to impair
cytoplasmic accumulation of unspliced RNA only slightly. Furthermore,
no decreases were observed in the stability of the unspliced RNA or in
the production of virus particles. Genomic RNA packaging, however, was
reduced by about 10-fold. Similar amounts of particles were produced by
cells containing the mutant and wild-type DNA, and all particles
contained similar levels of reverse transcriptase activity. The results
suggest that the region of the dr1 disrupted by the mutations plays a
role in genomic RNA packaging, although that packaging may not be the
only role for dr1.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Point Mutations in the Avian Sarcoma/Leukosis Virus
3' Untranslated Region Result in a Packaging Defect
and
*
Corresponding author. Mailing address: Department of
Molecular Biology and Microbiology, Tufts University School of
Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6750. Fax: (617) 636-0337. E-mail:
jcoffin_par{at}opal.tufts.edu.
Present address: Department of Animal Science, University of
Minnesota, St. Paul, MN 55108.
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