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Journal of Virology, January 1999, p. 297-306, Vol. 73, No. 1
Department of Microbiology, The Medical
School, University of Alabama at Birmingham, Birmingham, Alabama
Received 6 August 1998/Accepted 5 October 1998
The RNA-dependent RNA polymerase of vesicular stomatitis virus
(VSV), a nonsegmented negative-strand RNA virus, directs two discrete
RNA synthetic processes, transcription and replication. Available
evidence suggests that the two short extragenic regions at the
genomic termini, the 3' leader (Le) and the complement of the 5'
trailer (TrC), contain essential signals for these processes. We
examined the roles in transcription and replication of sequences in Le
and TrC by monitoring the effects of alterations to the termini of
subgenomic replicons, or infectious viruses, on these RNA
synthetic processes. Distinct elements in Le were found to be required
for transcription that were not required for replication. The promoter
for mRNA transcription was shown to include specific sequence elements within Le at positions 19 to 29 and 34 to 46, a
separate element at nucleotides 47 to 50, the nontranscribed leader-N gene junction. The sequence requirements for transcription within the Le region could not be supplied by sequences found at the equivalent positions in TrC. In contrast,
sequences from either Le or TrC functioned well to
signal replication, indicating that within the confines of the
VSV termini, the sequence requirements for
replication were less stringent. Deletions engineered at the termini
showed that the terminal 15 nucleotides of either Le or TrC allowed a
minimal level of replication. Within these confines, levels of
replication were affected by both the extent of complementarity between
the genomic termini and the involvement of the template in
transcription. In agreement with our previous observations, increasing
the extent of complementarity between the natural termini increased
levels of replication, and this effect was most operative at the
extreme genome ends. In addition, abolishing the use of Le as a
promoter for transcription enhanced replication. These analyses
(i) identified signals at the termini required for transcription and replication and (ii) showed that Le functions as
a less efficient promoter for replication than TrC at least in part
because of its essential role in transcription. Consequently,
these observations help explain the asymmetry of VSV replication
which results in the synthesis of more negative- than positive-sense
replication products in infected cells.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Regulation of RNA Synthesis by the Genomic Termini of Vesicular
Stomatitis Virus: Identification of Distinct Sequences Essential
for Transcription but Not Replication
*
Corresponding author. Mailing address: Department of
Microbiology, The Medical School, University of Alabama at Birmingham, BBRB17 Room 366, 845 19th St. South, Birmingham, AL 35294. Phone: (205) 934-0453. Fax: (205) 934-1636. E-mail:
gail_wertz{at}microbio.uab.edu.
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