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J. Biol. Chem., Vol. 281, Issue 19, 13075-13082, May 12, 2006
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Tax-dependent Displacement of Nucleosomes during Transcriptional Activation of Human T-Cell Leukemia Virus Type 1*
From the Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523-1870
The human T-cell leukemia virus type 1 (HTLV-1) is integrated into the host cell DNA and assembled into nucleosomes. Within the repressive chromatin environment, the virally encoded Tax protein mediates the recruitment of the coactivators CREB-binding protein/p300 to the HTLV-1 promoter, located within the long terminal repeats (LTRs) of the provirus. These proteins carry acetyltransferase activity that is essential for strong transcriptional activation of the virus in the context of chromatin. Consistent with this, the amino-terminal tails of nucleosomal histones at the viral promoter are acetylated in Tax-expressing cells. We have developed a system in which we transfect Tax into cells carrying integrated copies of the HTLV-1 LTR driving the luciferase gene to analyze changes in "activating" histone modifications at the LTR. Unexpectedly, Tax transactivation led to an apparent reduction of these modifications at the HTLV-1 promoter and downstream region that correlates with a similar reduction in histone H3 and linker histone H1. Micrococcal nuclease protection analysis showed that less LTR-luciferase DNA is nucleosomal in Tax-expressing cells. Furthermore, nucleosome depletion correlated with RNA polymerase II recruitment and loss of SWI/SNF. The M47 Tax mutant, deficient in HTLV-1 transcriptional activation, was also defective for nucleosome depletion. Although this mutant formed complexes with CREB and p300 at the HTLV-1 promoter in vivo, it was unable to mediate RNA polymerase II recruitment or SWI/SNF displacement. These results support a model in which nucleosomes are depleted from the LTR and transcribed region during Tax-mediated transcriptional activation and correlate RNA polymerase II recruitment with nucleosome depletion.
Received for publication, November 14, 2005 , and in revised form, March 17, 2006.
* This study was supported by NCI, National Institutes of Health Grants CA55035 (to J. K. N.) and CA87540 (to P. J. L. and J. K. N.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 Both authors contributed equally to this work.
2 Current address: Dept. of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27834.
3 To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870. Tel.: 970-491-5100; E-mail: Paul.Laybourn{at}colostate.edu.
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