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J Virol, August 1998, p. 6465-6474, Vol. 72, No. 8
Department of Biochemistry and Molecular
Biology1 and
Department of
Pathology,
Received 28 July 1997/Accepted 15 April 1998
Approximately 38% of human immunodeficiency virus type 1 (HIV-1)-infected patients within the Vancouver Lymphadenopathy-AIDS Study have proviruses bearing partial 15- to 34-nucleotide duplications upstream of the NF-
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Naturally Occurring Human Immunodeficiency Virus
Type 1 Long Terminal Repeats Have a Frequently Observed Duplication
That Binds RBF-2 and Represses Transcription

B binding sites within the 5' long terminal repeat (LTR). This most frequent naturally occurring length
polymorphism (MFNLP) of the HIV-1 5' LTR encompasses potential binding
sites for several candidate transcription factors, including
TCF-1
/hLEF, c-Ets, AP-4, and Ras-responsive binding factor 2 (RBF-2)
(M. C. Estable et al., J. Virol. 70:4053-4062, 1996). RBF-2
and an apparently related factor, RBF-1, bind to at least four
cis elements within the LTR which are required for full
transcriptional responsiveness to protein-tyrosine kinases and v-Ras
(B. Bell and I. Sadowski, Oncogene 13:2687-2697, 1996). Here we
demonstrate that representative MFNLPs from two patients specifically
bind RBF-2. In both cases, deletion of the MFNLP caused elevated
LTR-directed transcription in cells expressing RBF-2 but not in cells
with undetectable RBF-2. RBF-1, but not RBF-2, appears to contain the
Ets transcription factor family member GABP
/GABP
1. Taken together
with the fact that every MFNLP from a comparative study of over 500 LTR
sequences from 42 patients contains a predicted binding site for RBF-2, our data suggest that the MFNLP is selected in vivo because it provides
a duplicated RBF-2 cis element, which may limit
transcription in monocytes and activated T cells.
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, 2146 Health Sciences Mall, Vancouver, B.C. V6T 1Z3,
Canada. Phone: (604) 822-4524. Fax: (604) 822-5227. E-mail: sadowski{at}unixg.ubc.ca.
Present address: Institut de Genetique et de Biologie Moleculaire
et Cellulaire, CNRS/INSERM/ULP, College de France, Strasbourg, France.
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