Non-histone proteins in mononucleosomes and subnucleosomes

Area of Science:

• Molecular Biology
• Chromatin Structure

Background:

• Nucleosomes are the fundamental units of chromatin, composed of DNA and histone proteins.
• Non-histone proteins play crucial roles in regulating chromatin structure and function.
• High-mobility-group (HMG) proteins are a class of non-histone proteins known for their involvement in DNA binding and chromatin organization.

Purpose of the Study:

• To identify and characterize non-histone proteins within nucleosomes and subnucleosomes.
• To investigate the distribution and accessibility of these proteins in different chromatin fractions.
• To determine the role of non-histone proteins, particularly HMG proteins, in chromatin structure.

Main Methods:

• Sucrose gradient ultracentrifugation and polyacrylamide gel electrophoresis were used to separate nucleosomes and subnucleosomes.
• [3H]tryptophan incorporation was used to label non-histone proteins.
• Two-dimensional gel electrophoresis was employed to analyze non-histone protein composition.

Main Results:

• Non-histone proteins, including HMG proteins, were detected in nucleosome and subnucleosome fractions.
• Specific HMG proteins were found to be enriched in mononucleosome fractions (MN3 and MN2) and subnucleosome fractions (SN2 and SN3).
• A significant portion of HMG proteins were rapidly released from chromatin, indicating their accessibility to DNAase.

Conclusions:

• Non-histone proteins, especially HMG proteins, are integral components of nucleosomes and subnucleosomes.
• HMG proteins are located in regions of chromatin readily accessible to DNAase.
• Many non-histone proteins, including HMG proteins, likely interact with linker DNA in chromatin.