Histones are proteins around which DNA can wind. They play an important role in gene regulation in eukaryotic cells and in the Euryarchaea bacteria of the family Archaea. Histones are highly water soluble.
The six histone classes are H1, H2A, H2B, H3, H4, and Archaeal. All but the H1 and Archaeal classes create nucleosome core particles by wrapping DNA around their protein spools; the H1 then binds nucleosomes and entry and exit sites of the DNA. Histones and DNA assembled in this way are called chromatin.
Histones have several functions. They pack proteins so that they'll fit inside cell nuclei. Packed DNA are 50,000 times shorter than unpacked ones. They also perform a function in gene regulation; methylation causes tighter bindings to down-regulate or even inhibit gene transcription, while acetylation loosens bindings to help encourage transcription and translation. The other functions performed by histones are phosphorylation, ubiquitination, and ADP-ribosylation.
Histones were discovered in 1884 by Albrecht Kossel, though he dismissed them as of little importance. Only recently has the real function and value of the histone in protein regulation been understood.
Web Resources On Histones
Acetylation of Histones and Transcription-Related Factors
Book Resources On Histones
Histones and Other Basic Nuclear Proteins by Lubomir S. Hnilica et al
The structure and biological function of histones by Lubomir S Hnilica