The interaction of core histones with DNA: equilibrium binding studies

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Core histone proteins are essential components of chromatin.
• Understanding histone-DNA interactions is crucial for elucidating nucleosome structure and function.

Purpose of the Study:

• To investigate the binding characteristics of core histone proteins (H2a, H2b, H3, H4) to DNA.
• To determine the stages and cooperative nature of histone-DNA complex formation.
• To analyze the DNA protection role of the H3-H4 tetramer.

Main Methods:

• Salt-dependent dissociation and reassociation experiments of histone-DNA complexes.
• Measurement of binding thermodynamics (delta Go) at varying NaCl concentrations.
• Nuclease digestion of H3-H4 bound DNA fragments.

Main Results:

• Histone binding to DNA is a two-stage reversible process.
• H2a/H2b bind non-cooperatively between 0.7-1.2 M NaCl.
• H3/H4 bind cooperatively between 1.2-2.0 M NaCl, forming a tetramer that protects DNA fragments.
• H2a/H2b binding necessitates prior H3/H4 association.

Conclusions:

• The H3-H4 tetramer plays a critical role in nucleosome core particle formation.
• The H3-H4 tetramer's DNA protection capacity suggests it spans the entire nucleosome core.
• Histone binding demonstrates distinct cooperative and non-cooperative binding phases.