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Histone acetyltransferases regulate HIV-1 enhancer activity in vitro
P L Sheridan1, T P Mayall, E Verdin
1The Salk Institute for Biological Studies, La Jolla, California 92037-1099, USA.
Genes & Development
|February 7, 1998
Summary
Histone deacetylase inhibitors like trichostatin A (TSA) boost HIV-1 transcription by increasing histone acetylation. This enhances the number of active HIV-1 chromatin templates, facilitating transcription reinitiation.
Area of Science:
- Molecular Biology
- Epigenetics
- Virology
Background:
- Latent HIV-1 infection involves repressed transcription.
- Histone deacetylase (HDAC) inhibitors, such as trichostatin A (TSA), activate HIV-1 transcription.
- HDAC inhibition is linked to changes in chromatin structure, including nucleosome positioning.
Purpose of the Study:
- To investigate the mechanism by which TSA induces HIV-1 transcription on chromatin in vitro.
- To determine the role of histone acetylation and nucleosome remodeling in TSA-mediated HIV-1 activation.
- To assess the impact of TSA on the number and activity of HIV-1 transcription templates.
Main Methods:
- In vitro transcription assays using chromatin templates and naked DNA.
- Treatment with TSA, a specific histone deacetylase inhibitor.
- Analysis of histone H4 acetylation levels.
- Assessment of enhancer factor binding and nucleosome positioning (nuc-1).
- Limitation of transcription to single rounds using Sarkosyl to quantify active templates.
Main Results:
- TSA strongly induced HIV-1 transcription on chromatin, correlating with increased acetylated histone H4.
- TSA did not significantly alter enhancer factor binding or nuc-1 positioning on most templates.
- HIV-1 transcription on chromatin originated from a small number of highly active templates.
- TSA increased the number of active chromatin templates, while transcription on naked DNA was unaffected.
- Transcription reinitiation on chromatin was greatly facilitated by HIV-1 enhancer complexes.
Conclusions:
- TSA-induced HIV-1 transcription involves increased histone acetylation and a greater number of active chromatin templates.
- Chromatin remodeling of nuc-1 may require additional factors or occur only on transcriptionally competent templates.
- HIV-1 enhancer complexes are crucial for efficient transcription reinitiation on chromatin, acting at a rate-limiting step for histone acetylation or transcription factor modification.