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J Virol, July 1998, p. 5994-6003, Vol. 72, No. 7
School of Public Health, University of
California, Berkeley, California 94720
Received 27 May 1997/Accepted 9 April 1998
Bovine leukemia virus (BLV) is a member of the human T-cell
leukemia virus (HTLV)/BLV group of retroviruses. These viruses regulate their own transcription by producing Tax, a protein which activates the virus promoter region, the long terminal repeat (LTR). To
explore the molecular mechanisms involved in the
transactivation, we identified protein binding elements by in vivo
footprinting and analyzed their function by site- directed
mutagenesis. We used in vivo dimethyl sulfate footprinting by
ligation-mediated PCR to detect constitutive in vivo
protein-DNA interactions in a BLV-producing cell line,
Bat2Cl6. The U3 region and part of the R region
of the LTR were footprinted. In addition to the cis-acting elements (three cyclic AMP-responsive elements [CREs] and
two AP4 sites) reported by others to be important for Tax-mediated activation of the BLV LTR, we found footprints in regions flanking these elements and in the core promoter region. The importance of these
sites for transcriptional activation was studied by site-directed mutagenesis followed by promoter function analysis of the
mutants with a chloramphenicol acetyltransferase reporter system. Our data corroborate those of others showing that the CREs are necessary for transactivation of the LTR, and they identify two new functional sites not previously reported by others. We show that the middle region
of the BLV U3 contains multiple dual-functioning cis-acting elements which act as either positive or negative regulatory
elements depending on the cell type tested. This is the
first report of a functional mapping of the cis-acting
elements of a virus of the HTLV/BLV group.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
In Vivo Protein Binding and Functional Analysis of
cis-Acting Elements in the U3 Region of the Bovine
Leukemia Virus Long Terminal Repeat
and
*
Corresponding author. Mailing address: 140 Warren Hall,
School of Public Health, University of California, Berkeley, CA 94720. Phone: (510) 642-3870. Fax: (510) 642-6530. E-mail:
buehring{at}uclink4.berkeley.edu.
Present address: School of Dentistry, Department of Stomatology,
University of California, San Francisco, CA 94143.
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