Many explanations of histone biochemistry isn't quite elucidating for the undergraduate student. How does histone structure (dimers, octomers) relate to their specific functions as core or linker histones? Also, how do both linker and core histones interact within nucleosomes to ultimately regulate gene expression?
The core histones are H2A, H2B, H3, and H4, and the linker histones are H1 and H5. The structure of the nucleosome is well explained in wikipedia:
The core histones have a positive net charge, which facilitates the interaction with the negatively charged phosphate groups of DNA.
Apart from defining the nucleosome structure, the function of the core histones is regulatory: it can switch on/off gene expression by histone modifications like acetylation or methylation.
The gene expression is ON when there is:
• DNA demethylation
• histones acetylation
• H3K9 demethylation
The gene expression is OFF when there is:
• DNA methylation
// H3K4 demethylation is abbreviation for: Lysine 4 of H3 is demethylated.