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The [(G/C)3NN]n motif: a common DNA repeat that excludes nucleosomes
1Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill 27599-7295, USA.
Summary
Specific DNA sequences containing (G/C)3NN repeats strongly resist nucleosome formation. This finding has implications for understanding gene regulation in TATA-less genes.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nucleosomes, composed of DNA and histone proteins, are fundamental to chromosome structure and gene expression.
- Certain nucleotide sequences may influence DNA's ability to wrap around histones.
Purpose of the Study:
- To investigate whether a specific DNA sequence motif, [5'(G/C)3 NN3']n, can prevent nucleosome formation.
- To explore the biological relevance of such DNA sequences in gene regulation.
Main Methods:
- In vitro nucleosome reconstitution assays.
- Electron microscopy for structural analysis.
- Competitive reconstitution gel electrophoresis.
- Bioinformatic searches of the GenBank database.
Main Results:
- DNA fragments with 48 contiguous 5'-CCGNN-3' repeats strongly excluded nucleosomes.
- Nucleosome exclusion increased with the length of the (CCGNN) repeat sequence.
- These repeat sequences were found in promoter regions of TATA-less genes and co-localized with nuclease hypersensitive sites.
Conclusions:
- The (G/C)3NN motif significantly hinders nucleosome assembly, impacting DNA accessibility.
- These findings suggest a role for (G/C)3NN repeats in regulating gene expression, particularly in TATA-less gene promoters.