Гистон H2B: структура, функции и регуляция.

One of the five main histone proteins
Histone H2B is one of the 5 main histone proteins involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and long N terminal and C terminal tails, H2B is involved with the structure of the nucleosomes.

Histone H2B is a lightweight structural protein made of 126 amino acids. Many of these amino acids have a positive charge at cellular pH, which allows them to interact with the negatively charged phosphate groups in DNA. Along with a central globular domain, histone H2B has two flexible histone tails that extend outwards – one at the N terminal end and one at C terminal end. These are highly involved in condensing chromatin from the beads on a string conformation to a 30 nm fiber.

Histone H2B is a structural protein that helps organize eukaryotic DNA. It plays an important role in the biology of the nucleus where it is involved in the packaging and maintaining of chromosomes, Furthermore, acetylation of a specific lysine residue binds to bromine containing domains of certain transcription and chromatin regulatory proteins. This docking facilitates the recruitment of these proteins to the correct region of the chromosome. Ubiquitinated histone H2B is often found in regions of active transcription. While only a few isoforms of histone H2B have been studied in depth, researchers have found that histone H2B variants serve important roles. If certain variants stopped functioning, centromeres would not form correctly, genome integrity would be lost, and the DNA damage response would be silenced. Ubiquitinase RNF20/RNF40 specifically modifies histone H2B at position K120 and this modification is need for recruitment to damaged DNA of the factors necessary for repair by the pathways of homologous recombination and non homologous end joining. and the majority of them are found outside the globular domain of the nucleosome where amino acid residues are more accessible.

In histone H2B, a phosphorylated serine or threonine residue activates transcription. none of which contain introns. All of these genes are located in histone cluster 1 on chromosome 6 and cluster 2 and cluster 3 on chromosome 1. In each gene cluster, histone H2B genes share a promoter region with sequences that code for histone H2A. While all genes in the histone cluster are transcribed at high levels during S phase, individual histone H2B genes are also expressed at other times during the cell cycle. They are dually regulated by the cluster promoter sequences and their specific promoter sequences.