Histone H2B is one of the five major histones involved in eukaryotic chromatin structure. H2B has a major globular domain and long N- and C-terminal tails, which are related to the structure of the nucleosome.
Histone H2B is a light structural protein consisting of 126 amino acids. Many of these amino acids are positively charged at cellular pH, which enables them to interact with negatively charged phosphate groups in DNA. In addition to a central globular domain, histone H2B possesses two flexible histone tails that need to be verified to extend outwards, one at the N-terminus and one at the C-terminus. These are highly involved in condensing chromatin from the beaded conformation into 30-nanometer fibers. Similar to other histones, histone H2B has a unique histone fold optimized for histone-histone as well as histone-DNA interactions.
The two copies of histone H2B, together with two copies each of histone H2A, histone H3, and histone H4, form the octameric core of the nucleosome, providing structure to the DNA. To facilitate this formation, histone H2B first associates with histone H2A to form a heterodimer. Two of these heterodimers then combine with a heterotetramer consisting of histone H3 and histone H4, giving the nucleosome its characteristic disc shape. The deoxyribonucleic acid is then wrapped around the entire nucleosome as about 160 base pairs of DNA. Wrapping continues until all chromatin is wrapped with nucleosomes.
Histone H2B is a structural protein that helps organize eukaryotic DNA. It plays an important role in nuclear biology and is involved in the packaging and maintenance of chromosomes, transcriptional regulation, and DNA replication and repair. Histone H2B helps regulate chromatin structure and function through post-translational modifications and specialized histone variants.
Acetylation and ubiquitination are examples of two post-translational modifications that affect the function of histone H2B in specific ways. Hyperacetylation of histone tails facilitates the entry of DNA-binding proteins into chromatin by impairing histone DNA and nucleosome-nucleosome interactions. Although only a few histone H2B isoforms have been thoroughly studied, the researchers found that histone H2B variants play an important role. If some variants stop functioning, centromeres will not form properly, genome integrity will be lost, and the DNA damage response will be silenced. Specifically, in some lower eukaryotes, the histone H2B variant binds to a histone h2a variant called h2aZ, localizes to active genes, and supports transcription of these regions.