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Synthetic human beta-globin 5'HS2 constructs function as locus control regions only in multicopy transgene
1Laboratory of Gene Structure and Expression, National Institute for Medical Research, London, UK.
The EMBO Journal
|January 1, 1993
Summary
The beta-globin locus control region (LCR) requires multiple copies of its 5'HS2 core for gene expression, independent of integration site. Full activity relies on all factor binding sites, suggesting cooperative chromatin opening.
Area of Science:
- Molecular Biology
- Genetics
- Epigenetics
Background:
- Transgenes linked to the beta-globin locus control region (LCR) exhibit copy-dependent transcription.
- The 5'HS2 region of the LCR is crucial for this activity.
- Previous studies indicated the NF-E2 dimer binding site is not essential for LCR function.
Purpose of the Study:
- To investigate the role of other factor binding sites within the 5'HS2 core.
- To determine the minimal requirements for LCR activity in transgenic mice.
- To elucidate the mechanism of position-independent gene expression mediated by the LCR.
Main Methods:
- Analysis of synthetic 5'HS2 core constructs with point mutations in factor binding sites.
- Generation and analysis of transgenic mice carrying these constructs.
- Assessment of gene expression in MEL cells.
Main Results:
- The 5'HS2 core functions as a partially active LCR, requiring at least two copies in a concatamer for activity in transgenic mice.
- No single binding site within 5'HS2 is essential for position-independent expression.
- The H-BP factor was identified as upstream stimulatory factor (USF).
- Full enhancement by 5'HS2 core in MEL cells necessitates all factor binding sites.
Conclusions:
- The 5'HS2 core's activity is dependent on copy number and the presence of multiple factor binding sites.
- Co-localized 5'HS2 cores in a concatamer may interact to create an open chromatin state, facilitating LCR function.
- This cooperative chromatin remodeling is proposed as the basis for LCR activity.