Solution structure(s) of trinucleosomes from contrast variation SAXS.

Area of Science:

• Molecular Biology
• Biophysics
• Structural Biology

Background:

• Eukaryotic cells compact genomes using higher-order nucleosome structures.
• Understanding DNA storage and accessibility requires visualizing these structures.
• Nucleosome arrays model how DNA and protein interactions influence arrangement.

Purpose of the Study:

• To measure the solution conformation of trinucleosomes.
• To investigate the distance and orientation of linked nucleosomes.
• To understand how DNA sequence and protein partners affect nucleosome spacing.

Main Methods:

• Contrast variation small-angle X-ray scattering (CVSAXS) was used to analyze trinucleosome conformation in solution.
• DNA models incorporating sequence-dependent mechanical properties were employed.
• Monte Carlo techniques generated realistic structures for comparison with scattering data.

Main Results:

• Trinucleosomes in solution segregate into two main populations.
• These populations show flanking nucleosomes either stacked or nearly equilaterally separated.
• Results align with previously observed magnesium-dependent structures of trinucleosomes with shorter linkers.

Conclusions:

• CVSAXS effectively probes DNA conformation within protein-DNA complexes like trinucleosomes.
• Two distinct solution structures for trinucleosomes were identified.
• Findings provide insights into DNA packaging and accessibility influenced by protein-DNA interactions.