Previous Article | Next Article ![]()
Journal of Virology, September 2000, p. 8268-8276, Vol. 74, No. 18
Department of Microbiology, The Medical
School, University of Alabama at Birmingham, Birmingham, Alabama
35294
Received 28 April 2000/Accepted 20 June 2000
The nonsegmented negative-strand RNA (NNS) viruses have a
single-stranded RNA genome tightly encapsidated by the viral
nucleocapsid protein. The viral polymerase transcribes the genome
responding to specific gene-start and gene-end sequences to yield a
series of discrete monocistronic mRNAs. These mRNAs are not produced in
equimolar amounts; rather, their abundance reflects the position of the
gene with respect to the single 3'-proximal polymerase entry site.
Promoter-proximal genes are transcribed in greater abundance than more
distal genes due to a localized transcriptional attenuation at each
gene junction. In recent years, the application of reverse genetics to
the NNS viruses has allowed an examination of the role of the
gene-start and gene-end sequences in regulating mRNA synthesis. These
studies have defined specific sequences required for initiation, 5'
modification, termination, and polyadenylation of the viral mRNAs. In
the present report, working with Vesicular stomatitis
virus, the prototypic Rhabdovirus, we demonstrate
that a gene-end sequence must be positioned a minimal distance from a
gene-start sequence for the polymerase to efficiently terminate transcription. Gene-end sequences were almost completely ignored in
transcriptional units less than 51 nucleotides. Transcriptional units
of 51 to 64 nucleotides allowed termination at the gene-end sequence,
although the frequency with which polymerase failed to terminate and
instead read through the gene-end sequence to generate a bicistronic
transcript was enhanced compared to the observed 1 to 3% for wild-type
viral mRNAs. In all instances, failure to terminate at the gene end
prevented initiation at the downstream gene start site. In contrast to
this size requirement, we show that the sequence between the gene-start
and gene-end signals, or its potential to adopt an RNA secondary
structure, had only a minor effect on the efficiency with which
polymerase terminated transcription. We suggest three possible
explanations for the failure of polymerase to terminate transcription
in response to a gene-end sequence positioned close to a gene-start
sequence which contribute to our emerging picture of the mechanism of
transcriptional regulation in this group of viruses.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Identification of a Minimal Size Requirement for Termination
of Vesicular Stomatitis Virus mRNA: Implications for the
Mechanism of Transcription
*
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.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»