Histonach

Histonach are a family of small, highly basic nuclear proteins that package and organize DNA in eukaryotic cells. They form the core components of chromatin, around which DNA is wrapped to regulate access to genetic information. The core histon group comprises H2A, H2B, H3, and H4, which assemble into an octamer. About 146 base pairs of DNA wrap around this octamer to form a nucleosome, the fundamental unit of chromatin. The linker histone H1 binds the DNA between nucleosomes and facilitates higher-order chromatin folding.

Histonach are characterized by a high content of lysine and arginine residues, giving them a positive charge that helps neutralize the negatively charged DNA backbone. The amino-terminal tails of histonach protrude from the nucleosome core and are rich in modifiable residues. Post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitination on these tails influence chromatin structure and gene expression, a concept central to the histone code hypothesis.

Variants of histonach, including H2A.Z, H3.3, and CENP-A, confer specialized functions at promoters, regulatory elements, or centromeres. The assembly and disassembly of histonach during DNA replication and repair are guided by histone chaperones, such as CAF-1 and HIRA, which mediate histone deposition and turnover.

Histonach are highly conserved across eukaryotes, with archaeal organisms possessing histone-like proteins that resemble simplified versions of the eukaryotic histonach. Dysregulation of histonach modifications and variant incorporation is implicated in development and disease, notably in cancer and other epigenetic disorders.