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Transactivation functions facilitate the disruption of chromatin structure by estrogen receptor derivatives in vivo
T A Pham1, Y P Hwung, D P McDonnell
1Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Abstract:
The activation of gene transcription by nuclear receptors is invariably associated with alterations in chromatin structure at hormone-responsive elements of target genes. To identify the molecular functions underlying receptor-mediated chromatin structure alterations we have evaluated the effects of DNA binding and transactivation of estrogen receptor derivatives on the promoter chromatin structure of estrogen-responsive reporter minichromosomes in Saccharomyces cerevisiae. We report here that the DNase I-hypersensitive chromatin structure at the promoter region is not simply a consequence of estrogen receptor binding to estrogen-responsive elements but is greatly enhanced by transactivation functions. These chromatin structure alterations are dependent on the presence of more than one estrogen-responsive element as well as downstream promoter sequences and appear to be correlated with transcriptional competence of the promoter. Our results imply that a disruption of chromatin structure at promoters is associated with the establishment of active transcription complexes. Since RNA polymerase cannot initiate transcription on nucleosomal DNA in vitro (Lorch, Y., Lapointe, J.W., and Kornberg, R.D. (1987) Cell 49, 203-210) this local disruption of chromatin structure may represent a nucleosome-free window, allowing initiation to occur in vivo.
Insights
Estrogen receptor binding and transactivation enhance chromatin structure alterations at gene promoters. This disruption creates a nucleosome-free window essential for initiating transcription in vivo.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nuclear receptors activate gene transcription through chromatin structure modifications.
- Estrogen receptor (ER) binding to DNA alters chromatin at target genes.
- Understanding these molecular mechanisms is crucial for gene regulation studies.
Purpose of the Study:
- To investigate the role of DNA binding and transactivation by ER derivatives.
- To analyze ER-mediated chromatin structure changes at estrogen-responsive reporter minichromosomes.
- To elucidate the molecular functions underlying receptor-mediated chromatin alterations.
Main Methods:
- Utilized Saccharomyces cerevisiae as a model system.
- Employed reporter minichromosomes with estrogen-responsive elements.
- Evaluated DNase I-hypersensitive chromatin structure in response to ER derivatives.
Main Results:
- Promoter chromatin structure alterations are enhanced by ER transactivation functions, not just DNA binding.
- These chromatin changes depend on multiple estrogen-responsive elements and downstream promoter sequences.
- Chromatin alterations correlate with promoter transcriptional competence.
Conclusions:
- Receptor-mediated disruption of chromatin structure is linked to active transcription complex formation.
- This local chromatin disruption likely creates a nucleosome-free window for transcription initiation.
- Findings suggest a mechanism for how nuclear receptors establish transcriptional competence.