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Mol Cell Biol, May 1998, p. 2535-2544, Vol. 18, No. 5
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Transcriptional Activation of the Integrated Chromatin-Associated Human Immunodeficiency Virus Type 1 Promoter

Aboubaker El Kharroubi, Graziella Piras,dagger Ralf Zensen, and Malcolm A. Martin*

Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892

Received 2 October 1997/Returned for modification 7 November 1997/Accepted 4 February 1998

The regulation of human immunodeficiency virus type 1 (HIV-1) gene expression involves a complex interplay between cellular transcription factors, chromatin-associated proviral DNA, and the virus-encoded transactivator protein, Tat. Here we show that Tat transactivates the integrated HIV-1 long terminal repeat (LTR), even in the absence of detectable basal promoter activity, and this transcriptional activation is accompanied by chromatin remodeling downstream of the transcription initiation site, as monitored by increased accessibility to restriction endonucleases. However, with an integrated promoter lacking both Sp1 and NF-kappa B sites, Tat was unable to either activate transcription or induce changes in chromatin structure even when it was tethered to the HIV-1 core promoter upstream of the TATA box. Tat responsiveness was observed only when Sp1 or NF-kappa B was bound to the promoter, implying that Tat functions subsequent to the formation of a specific transcription initiation complex. Unlike Tat, NF-kappa B failed to stimulate the integrated transcriptionally silent HIV-1 promoter. Histone acetylation renders the inactive HIV-1 LTR responsive to NF-kappa B, indicating that a suppressive chromatin structure must be remodeled prior to transcriptional activation by NF-kappa B. Taken together, these results suggest that Sp1 and NF-kappa B are required for the assembly of transcriptional complexes on the integrated viral promoter exhibiting a continuum of basal activities, all of which are fully responsive to Tat.

* Corresponding author. Mailing address: Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bldg. 4, Room 315, 4 Center Dr., Bethesda, MD 20892. Phone: (301) 496-4012. Fax: (301) 402-0226. E-mail: maln{at}nih.gov.

dagger Present address: Mammalian Developmental Biology Laboratory, ABL Basic Research Program, Frederick, MD 21702.

Mol Cell Biol, May 1998, p. 2535-2544, Vol. 18, No. 5
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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