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Journal of Virology, November 1999, p. 9039-9052, Vol. 73, No. 11
Department of
Microbiology1 and Department of Internal
Medicine,2 College of Medicine, University
of Iowa, Iowa City, Iowa 52242
Received 18 June 1999/Accepted 13 August 1999
The region of the human cytomegalovirus (CMV) genome between the
UL127 open reading frame and the major immediate-early (MIE) enhancer
is referred to as the unique region. DNase I protection analysis with
human cell nuclear extracts demonstrated multiple protein binding sites
in this region of the viral genome (P. Ghazal, H. Lubon, C. Reynolds-Kohler, L. Hennighausen, and J. A. Nelson, Virology
174:18-25, 1990). However, the function of this region in the context
of the viral genome is not known. In wild-type human CMV-infected human
fibroblasts, cells permissive for viral replication, there is little to
no transcription from UL127. We determined that the unique region
prevented transcription from the UL127 promoter but had no effect on
the divergent MIE promoter. In transient-transfection assays, the basal
level of expression from the UL127 promoter increased significantly
when the wild-type unique sequences were mutated. In recombinant
viruses with similar mutations in the unique region, expression from
the UL127 promoter occurred only after de novo viral protein synthesis,
typical of an early viral promoter. A 111-bp deletion-substitution of
the unique sequence caused approximately a 20-fold increase in the steady-state level of RNA from the UL127 promoter and a 245-fold increase in the expression of a downstream indicator gene. This viral
negative regulatory region was also mutated at approximately 50-bp
regions proximal and distal to the UL127 promoter. Although some
repressive effects were detected in the distal region, mutations of the
region proximal to the UL127 promoter had the most significant effects
on transcription. Within the proximal and distal regions, there are
potential cis sites for known eucaryotic transcriptional repressor proteins. This region may also bind unknown viral proteins. We propose that the unique region upstream of the UL127 promoter and
the MIE enhancer negatively regulates the expression from the UL127
promoter in permissive human fibroblast cells. This region may be a
regulatory boundary preventing the effects of the very strong MIE
enhancer on this promoter.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
A Strong Negative Transcriptional Regulatory Region
between the Human Cytomegalovirus UL127 Gene and the Major
Immediate-Early Enhancer
*
Corresponding author. Mailing address: Department of
Microbiology, College of Medicine, The University of Iowa, 3772 Bowen Science Bldg., Iowa City, IA 52242-1109. Phone: (319) 335-7792. Fax: (319) 335-9006. E-mail: mark-stinski{at}uiowa.edu.
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