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Journal of Virology, November 2001, p. 10149-10160, Vol. 75, No. 21
Department of Microbiology, Osaka University
Medical School C1,1 and Division of
Advanced Medical Bacteriology, Osaka University Medical School
G5,2 Suita, Osaka 565-0871, Japan
Received 19 March 2001/Accepted 20 July 2001
An immediate-early (IE) gene of human herpesvirus 6 (HHV-6), U95,
has similarity at the amino acid level to the murine cytomegalovirus (MCMV) IE2 gene and is related to the human cytomegalovirus (HCMV) US22
gene family. Sequence analyses of U95 cDNA clones revealed that the
transcription start site was located about 1.6 kbp upstream of the
putative initiating ATG and that the transcript consisted of two exons.
A single intron extended from nucleotides 142589 to 144229, which
contained ORF U94. A protein with a molecular mass of about 120 kDa was
translated from this cDNA clone in an in vitro
transcription-translation assay. The transcription start site was found
to be 220 bp downstream of the R3 region by primer extension analysis.
HHV-6 has three repetitive elements, R1, R2, and R3, in or near the
IE-A locus. R3 is composed of 24 copies of a 104- to 107-bp sequence
element, which contains multiple putative binding sites for cellular
transcription factors such as AP2 and NF-
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.21.10149-10160.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The R3 Region, One of Three Major Repetitive
Regions of Human Herpesvirus 6, Is a Strong Enhancer of
Immediate-Early Gene U95
B, and its biological
significance has yet to be elucidated. The region between
710 and +46
relative to the transcription start site of U95 was analyzed in this
study. Deletion from
710 to
396, corresponding to three copies of
an R3 unit, decreased the promoter activity by 15-fold, and
coexpression of I
B
(S32A/S36A) repressed it to almost the same
level. Electrophoretic mobility shift assays showed that NF-
B family
members p50 and c-Rel bound to NF-
B sites derived from the R3
region. These results demonstrate that R3 strongly enhances the U95
promoter activity and that NF-
B and binding sites for NF-
B in the
R3 region play an important role in its activation. Because U95
promoter activity correlated with the number of R3 units, which each
contained an NF-
B site, the repetitive organization of R3 is
important for regulating U95 transcription.
*
Corresponding author. Mailing address: Department of
Microbiology, Osaka University Medical School C1, 2-2 Yamada-Oka,
Suita, Osaka 565-0871, Japan. Phone: 81-6-6879-3323. Fax:
81-6-6879-3329. E-mail:
simamoto{at}micro.med.osaka-u.ac.jp.
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