H2AH2B

H2AH2B refers to the histone H2A–H2B heterodimer, a core component of eukaryotic nucleosomes. It is formed by non-identical histone proteins H2A and H2B and acts as one of the two available dimers that regulate DNA packaging in chromatin. Together with a histone H3–H4 tetramer, two H2A–H2B dimers assemble to form the nucleosome core particle, around which approximately 147 base pairs of DNA are wrapped. The H2A–H2B dimer contributes to the outer surface of the nucleosome and participates in interactions with DNA as well as with other chromatin factors.

Structural characteristics include the histone fold domains shared by H2A and H2B, which mediate dimerization and contacts with DNA. The dimer–dimer interface creates a stable core within the octamer, enabling the dynamic remodeling of nucleosomes during processes such as transcription, replication, and repair. Post-translational modifications on the H2A and H2B tails, including acetylation, ubiquitination, and methylation, influence nucleosome stability and accessibility of DNA to transcription factors and repair enzymes.

Biological dynamics involve histone chaperones and remodeling complexes that regulate the deposition and exchange of H2A–H2B dimers. Replication-coupled assembly commonly uses factors such as CAF-1, while replication-independent exchange can involve chaperones like Nap1 and complexes such as FACT. Variants of H2A and H2B exist across species (for example H2A.Z and H2A.X) and can alter nucleosome stability and gene regulation.

H2A–H2B is essential for chromatin structure and genome function, with perturbations affecting gene expression, DNA damage response, and cellular viability.