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HMG 14/17 binding affinities and DNAase I sensitivities of nucleoprotein particles
Abstract:
We show that ordinary (bulk) chicken erythrocyte nucleosomes are digested more rapidly by DNAase I when they are associated with high mobility group (HMG) proteins 14/17. Digestion of HMG 14/17-nucleosome complexes, under conditions where the DNA in control nucleosomes is digested to 10 to 20% acid solubility, results in a particular depletion of single-strand DNA fragments greater than 80 nucleotides in length, relative to the DNA fragments produced from control nucleosomes. Additionally, we show that staphylococcal nuclease digests of H1/H5-depleted chromatin contain an abundant subclass of nucleosomes that are not present in appreciable amounts in digests of native chromatin. These nucleosomes contain longer lengths of DNA and have lower electrophoretic mobilities than core particles. HMG 14/17 associates highly preferentially with these nucleosomes and renders them sensitive to DNAase I, similar to what has been found for active nucleosomes.
Insights
High mobility group (HMG) proteins 14/17 enhance DNAase I digestion of chicken erythrocyte nucleosomes. These HMG proteins preferentially bind to specific nucleosomes, increasing their sensitivity to DNAase I digestion.
Area of Science:
- Molecular Biology
- Chromatin Structure
- Biochemistry
Background:
- Nucleosomes are the basic units of DNA packaging in eukaryotes.
- High mobility group (HMG) proteins are involved in chromatin structure and DNA processing.
- Specific nucleosome populations are associated with active genes.
Purpose of the Study:
- To investigate the role of HMG proteins 14/17 in nucleosome structure and DNA accessibility.
- To determine if HMG proteins 14/17 influence the susceptibility of nucleosomes to enzymatic digestion.
- To characterize nucleosome subclasses in H1/H5-depleted chromatin.
Main Methods:
- Enzymatic digestion of chicken erythrocyte nucleosomes and chromatin using DNAase I and staphylococcal nuclease.
- Analysis of DNA fragment lengths and electrophoretic mobilities of digested nucleosomes.
- Assessing the association of HMG proteins 14/17 with specific nucleosome populations.
Main Results:
- HMG proteins 14/17 increase the rate of DNAase I digestion of bulk chicken erythrocyte nucleosomes.
- HMG 14/17-nucleosome complexes show a depletion of DNA fragments >80 nucleotides after DNAase I digestion.
- Staphylococcal nuclease digests of H1/H5-depleted chromatin reveal a unique nucleosome subclass with longer DNA and lower mobility.
- HMG 14/17 proteins preferentially associate with this subclass, rendering them DNAase I sensitive.
Conclusions:
- HMG proteins 14/17 play a role in modulating nucleosome structure and DNA accessibility.
- The preferential association of HMG 14/17 with specific nucleosomes suggests a role in regulating gene activity.
- These findings provide insights into the functional significance of HMG proteins in chromatin organization.