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Journal of Virology, November 1998, p. 8961-8970, Vol. 72, No. 11
Department of Molecular Biology and
Biochemistry and Cancer Research Institute, University of
California, Irvine, California 92697-3900
Received 29 April 1998/Accepted 15 July 1998
The enhancer sequences in the Moloney murine leukemia virus
(M-MuLV) long terminal repeat (LTR) are of considerable interest since
they are crucial for virus replication and the ability of the virus to
induce T lymphomas. While extensive studies have identified numerous
nuclear factors that can potentially bind to M-MuLV enhancer DNA in
vitro, it has not been made clear which of these factors are bound in
vivo. To address this problem, we carried out in vivo footprinting of
the M-MuLV enhancer in infected cells by in vivo treatment with
dimethyl sulfate (DMS) followed by visualization through
ligation-mediated PCR (LMPCR) and gel electrophoresis. In vivo
DMS-LMPCR footprinting of the upstream LTR revealed evidence for factor
binding at several previously characterized motifs. In particular,
protection of guanines in the central LVb/Ets and Core sites within the
75-bp repeats was detected in infected NIH 3T3 fibroblasts, Ti-6
lymphoid cells, and thymic tumor cells. In contrast, factor binding at
the NF-1 sites was found in infected fibroblasts but not in T-lymphoid cells. These results are consistent with the results of previous experiments indicating the importance of the LVb/Ets and Core sequences
for many retroviruses and the biological importance especially of the
NF-1 sites in fibroblasts and T-lymphoid cells. No evidence for factor
binding to the glucocorticoid responsive element and LVa sites was
found. Additional sites of protein binding included a region in the
GC-rich sequences downstream of the 75-bp repeats (only in
fibroblasts), a hypersensitive guanine on the minus strand in the LVc
site (only in T-lymphoid cells), and a region upstream of the 75-bp
repeats. These experiments provide concrete evidence for the
differential in vivo binding of nuclear factors to the M-MuLV enhancers
in different cell types.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
In Vivo Footprinting of the Enhancer Sequences in the Upstream
Long Terminal Repeat of Moloney Murine Leukemia Virus: Differential
Binding of Nuclear Factors in Different Cell Types
*
Corresponding author. Mailing address: Department of
Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900. Phone: (949) 824-5554. Fax: (949) 824-4023. E-mail: hyfan{at}uci.edu.
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