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J Virol, May 1998, p. 4072-4079, Vol. 72, No. 5
Institute of Biological Chemistry, Washington
State University, Pullman, Washington 99164-6340
Received 26 September 1997/Accepted 26 January 1998
The 3'-terminal 350 nucleotides of the tobacco etch potyvirus (TEV)
genome span the end of the capsid protein (CP)-coding sequence and the
3' nontranslated region (NTR). The CP-coding sequence within this
region contains a 105-nucleotide cis-active element
required for genome replication (S. Mahajan, V. V. Dolja, and
J. C. Carrington, J. Virol. 70:4370-4379, 1996). To
investigate the sequence and secondary structure requirements within
the CP cis-active region and the 3' NTR, a systematic
linker-scanning mutagenesis analysis was done. Forty-six mutations,
each with two to six nucleotide substitutions, were introduced at
consecutive hexanucleotide positions in the genome of a recombinant TEV
strain expressing a reporter protein (
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Secondary Structures in the Capsid Protein Coding
Sequence and 3' Nontranslated Region Involved in Amplification of
the Tobacco Etch Virus Genome
-glucuronidase). Genome
amplification activity of each mutant in the protoplast cell culture
system was measured. Mutations that severely debilitated genome
amplification were identified throughout the CP-coding
cis-active sequence and at several distinct locations
within the 3' NTR. However, based on a computer model of RNA folding,
mutations that had the most severe effects mapped to regions that were
predicted to form base-paired secondary structures. Linker-scanning
mutations predicted to affect either strand of a base-paired structure
within the CP-coding cis-active sequence, a base-paired
structure between two segments of the CP-coding cis-active
sequence and a contiguous 14-nucleotide segment of the 3' NTR, and a
base-paired structure near the 3' terminus of the 3' NTR inactivated
genome amplification. Compensatory mutations that restored base pair
interactions in each of these regions restored amplification activity,
although to differing levels depending on the structure restored. These
data reveal that the 3' terminus of the TEV genome consists of a series
of functionally discrete sequences and secondary structures and that the CP-coding sequence and 3' NTR are coadapted for genome
amplification function through a requirement for base pair
interactions.
*
Corresponding author. Mailing address: Institute of
Biological Chemistry, Washington State University, Pullman, WA
99164-6340. Phone: (509) 335-2477. Fax: (509) 335-2482. E-mail:
carrington{at}wsu.edu.
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